diff --git a/backend/UniVerse.Application/DTOs/Achievements/AchievementDtos.cs b/backend/UniVerse.Application/DTOs/Achievements/AchievementDtos.cs
new file mode 100644
index 0000000..203cd66
--- /dev/null
+++ b/backend/UniVerse.Application/DTOs/Achievements/AchievementDtos.cs
@@ -0,0 +1,36 @@
+namespace UniVerse.Application.DTOs.Achievements;
+
+public record AchievementDto(
+    int Id,
+    string Name,
+    string? Description,
+    string? IconUrl,
+    int XpReward,
+    int CoinReward,
+    string? Condition,
+    DateTime CreatedAt
+);
+
+public record UserAchievementDto(
+    int Id,
+    AchievementDto Achievement,
+    DateTime AwardedAt
+);
+
+public record CreateAchievementRequest(
+    string Name,
+    string? Description,
+    string? IconUrl,
+    int XpReward,
+    int CoinReward,
+    string? Condition
+);
+
+public record UpdateAchievementRequest(
+    string Name,
+    string? Description,
+    string? IconUrl,
+    int XpReward,
+    int CoinReward,
+    string? Condition
+);
diff --git a/backend/UniVerse.Application/DTOs/Auth/AuthDtos.cs b/backend/UniVerse.Application/DTOs/Auth/AuthDtos.cs
new file mode 100644
index 0000000..e7c5f3c
--- /dev/null
+++ b/backend/UniVerse.Application/DTOs/Auth/AuthDtos.cs
@@ -0,0 +1,11 @@
+using UniVerse.Domain.Enums;
+
+namespace UniVerse.Application.DTOs.Auth;
+
+public record AuthResponse(string AccessToken, DateTime ExpiresAt, UserAuthDto User);
+
+public record UserAuthDto(int Id, string Email, string? DisplayName, UserRole Role);
+
+public record LoginMicrosoftRequest(string AuthorizationCode);
+
+public record DevLoginRequest(string Email, string? DisplayName = null, UserRole Role = UserRole.Student);
diff --git a/backend/UniVerse.Application/DTOs/Common/PaginationDtos.cs b/backend/UniVerse.Application/DTOs/Common/PaginationDtos.cs
new file mode 100644
index 0000000..aa47e0e
--- /dev/null
+++ b/backend/UniVerse.Application/DTOs/Common/PaginationDtos.cs
@@ -0,0 +1,18 @@
+namespace UniVerse.Application.DTOs.Common;
+
+public record PaginationRequest(int Page = 1, int PageSize = 20);
+
+public record PagedResult<T>(
+    List<T> Items,
+    int TotalCount,
+    int Page,
+    int PageSize,
+    int TotalPages
+)
+{
+    public static PagedResult<T> Create(List<T> items, int totalCount, int page, int pageSize)
+    {
+        var totalPages = (int)Math.Ceiling(totalCount / (double)pageSize);
+        return new PagedResult<T>(items, totalCount, page, pageSize, totalPages);
+    }
+}
diff --git a/backend/UniVerse.Application/DTOs/Courses/CourseDtos.cs b/backend/UniVerse.Application/DTOs/Courses/CourseDtos.cs
new file mode 100644
index 0000000..bc533d8
--- /dev/null
+++ b/backend/UniVerse.Application/DTOs/Courses/CourseDtos.cs
@@ -0,0 +1,24 @@
+using UniVerse.Application.DTOs.Tags;
+
+namespace UniVerse.Application.DTOs.Courses;
+
+public record CourseDto(
+    int Id,
+    string Name,
+    string? Description,
+    bool IsSynced,
+    List<TagDto> Tags,
+    DateTime CreatedAt
+);
+
+public record CreateCourseRequest(string Name, string? Description);
+
+public record UpdateCourseRequest(string Name, string? Description);
+
+public record CourseFilterRequest(
+    int? TagId,
+    string? Search,
+    bool? IsSynced,
+    int Page = 1,
+    int PageSize = 20
+);
diff --git a/backend/UniVerse.Application/DTOs/Gamification/GamificationDtos.cs b/backend/UniVerse.Application/DTOs/Gamification/GamificationDtos.cs
new file mode 100644
index 0000000..3248165
--- /dev/null
+++ b/backend/UniVerse.Application/DTOs/Gamification/GamificationDtos.cs
@@ -0,0 +1,13 @@
+using UniVerse.Domain.Enums;
+
+namespace UniVerse.Application.DTOs.Gamification;
+
+public record CoinTransactionDto(
+    int Id,
+    int Amount,
+    CoinTransactionType Type,
+    int? ReviewId,
+    int? AchievementId,
+    string? Description,
+    DateTime CreatedAt
+);
diff --git a/backend/UniVerse.Application/DTOs/Lectures/LectureDtos.cs b/backend/UniVerse.Application/DTOs/Lectures/LectureDtos.cs
new file mode 100644
index 0000000..37f3340
--- /dev/null
+++ b/backend/UniVerse.Application/DTOs/Lectures/LectureDtos.cs
@@ -0,0 +1,86 @@
+using UniVerse.Domain.Enums;
+
+namespace UniVerse.Application.DTOs.Lectures;
+
+public record LectureDto(
+    int Id,
+    int CourseId,
+    string CourseName,
+    int? TeacherId,
+    string? TeacherName,
+    int? LocationId,
+    string? LocationName,
+    string Title,
+    string? Description,
+    LectureFormat Format,
+    DateTime StartsAt,
+    DateTime EndsAt,
+    bool IsOpen,
+    int MaxEnrollments,
+    int EnrollmentsCount,
+    string? OnlineUrl,
+    DateTime CreatedAt
+);
+
+public record LectureDetailDto(
+    int Id,
+    int CourseId,
+    string CourseName,
+    int? TeacherId,
+    string? TeacherName,
+    int? LocationId,
+    string? LocationName,
+    string Title,
+    string? Description,
+    LectureFormat Format,
+    DateTime StartsAt,
+    DateTime EndsAt,
+    bool IsOpen,
+    int MaxEnrollments,
+    int EnrollmentsCount,
+    string? OnlineUrl,
+    DateTime CreatedAt,
+    bool IsEnrolled
+);
+
+public record CreateLectureRequest(
+    int CourseId,
+    int? TeacherId,
+    int? LocationId,
+    string Title,
+    string? Description,
+    LectureFormat Format,
+    DateTime StartsAt,
+    DateTime EndsAt,
+    bool IsOpen,
+    int MaxEnrollments,
+    string? OnlineUrl
+);
+
+public record UpdateLectureRequest(
+    int? TeacherId,
+    int? LocationId,
+    string Title,
+    string? Description,
+    LectureFormat Format,
+    DateTime StartsAt,
+    DateTime EndsAt,
+    bool IsOpen,
+    int MaxEnrollments,
+    string? OnlineUrl
+);
+
+public record LectureFilterRequest(
+    DateOnly? DateFrom,
+    DateOnly? DateTo,
+    int? CourseId,
+    int? TeacherId,
+    LectureFormat? Format,
+    bool? IsOpen,
+    int? TagId,
+    string? Search,
+    int Page = 1,
+    int PageSize = 20
+);
+
+public record EnrollmentDto(int Id, int UserId, string? UserName, string? UserEmail, bool Attended, DateTime CreatedAt);
diff --git a/backend/UniVerse.Application/DTOs/Locations/LocationDtos.cs b/backend/UniVerse.Application/DTOs/Locations/LocationDtos.cs
new file mode 100644
index 0000000..60470ae
--- /dev/null
+++ b/backend/UniVerse.Application/DTOs/Locations/LocationDtos.cs
@@ -0,0 +1,7 @@
+namespace UniVerse.Application.DTOs.Locations;
+
+public record LocationDto(int Id, string Name, string? Building, string? Room, string? Address, DateTime CreatedAt);
+
+public record CreateLocationRequest(string Name, string? Building, string? Room, string? Address);
+
+public record UpdateLocationRequest(string Name, string? Building, string? Room, string? Address);
diff --git a/backend/UniVerse.Application/DTOs/Reviews/ReviewDtos.cs b/backend/UniVerse.Application/DTOs/Reviews/ReviewDtos.cs
new file mode 100644
index 0000000..416ee41
--- /dev/null
+++ b/backend/UniVerse.Application/DTOs/Reviews/ReviewDtos.cs
@@ -0,0 +1,23 @@
+using UniVerse.Domain.Enums;
+
+namespace UniVerse.Application.DTOs.Reviews;
+
+public record ReviewDto(
+    int Id,
+    int LectureId,
+    string? LectureTitle,
+    int UserId,
+    string? UserName,
+    ReviewRating Rating,
+    string? Text,
+    ReviewLlmStatus LlmStatus,
+    ReviewSentiment? Sentiment,
+    double? QualityScore,
+    bool? IsInformative,
+    string[]? LlmTags,
+    DateTime CreatedAt
+);
+
+public record CreateReviewRequest(int LectureId, ReviewRating Rating, string? Text);
+
+public record UpdateReviewRequest(ReviewRating Rating, string? Text);
diff --git a/backend/UniVerse.Application/DTOs/Sync/SyncDtos.cs b/backend/UniVerse.Application/DTOs/Sync/SyncDtos.cs
new file mode 100644
index 0000000..c55263e
--- /dev/null
+++ b/backend/UniVerse.Application/DTOs/Sync/SyncDtos.cs
@@ -0,0 +1,14 @@
+namespace UniVerse.Application.DTOs.Sync;
+
+public record SyncScheduleRequest(
+    string? SpecialtyCode,
+    DateTime? TimeMin,
+    DateTime? TimeMax,
+    string? TypeId
+);
+
+public record SyncResultDto(int Created, int Updated, int Skipped, string? Error);
+
+public record SyncStatusDto(DateTime? LastSyncAt, string Status, SyncResultDto? LastResult);
+
+public record EmployeeDto(string? Id, string FullName, string? Department);
diff --git a/backend/UniVerse.Application/DTOs/Tags/TagDtos.cs b/backend/UniVerse.Application/DTOs/Tags/TagDtos.cs
new file mode 100644
index 0000000..60e98c4
--- /dev/null
+++ b/backend/UniVerse.Application/DTOs/Tags/TagDtos.cs
@@ -0,0 +1,11 @@
+using UniVerse.Domain.Enums;
+
+namespace UniVerse.Application.DTOs.Tags;
+
+public record TagDto(int Id, string Name, TagType Type, int? ParentId, DateTime CreatedAt);
+
+public record TagTreeDto(int Id, string Name, TagType Type, List<TagTreeDto> Children);
+
+public record CreateTagRequest(string Name, TagType Type, int? ParentId);
+
+public record UpdateTagRequest(string Name, TagType Type, int? ParentId);
diff --git a/backend/UniVerse.Application/DTOs/Users/UserDtos.cs b/backend/UniVerse.Application/DTOs/Users/UserDtos.cs
new file mode 100644
index 0000000..2a79aa9
--- /dev/null
+++ b/backend/UniVerse.Application/DTOs/Users/UserDtos.cs
@@ -0,0 +1,55 @@
+using UniVerse.Domain.Enums;
+
+namespace UniVerse.Application.DTOs.Users;
+
+public record UserDto(
+    int Id,
+    string Email,
+    string? DisplayName,
+    string? AvatarUrl,
+    UserRole Role,
+    bool IsActive,
+    int Xp,
+    int Coins,
+    int Level,
+    DateTime CreatedAt
+);
+
+public record UserStatsDto(
+    int TotalLectures,
+    int AttendedLectures,
+    int TotalReviews,
+    int Xp,
+    int Coins,
+    int Level,
+    int AchievementsCount
+);
+
+public record UpdateUserRequest(
+    string? DisplayName,
+    string? AvatarUrl
+);
+
+public record UserFilterRequest(
+    string? Search,
+    UserRole? Role,
+    bool? IsActive,
+    int Page = 1,
+    int PageSize = 20
+);
+
+public record StudentProfileDto(
+    int Id,
+    string? StudentId,
+    string? GroupName,
+    int? EnrollmentYear,
+    string? Faculty,
+    string? Specialty
+);
+
+public record TeacherProfileDto(
+    int Id,
+    string? Department,
+    string? Title,
+    string? Bio
+);
diff --git a/backend/UniVerse.Application/Interfaces/IAchievementService.cs b/backend/UniVerse.Application/Interfaces/IAchievementService.cs
new file mode 100644
index 0000000..3e3b8d3
--- /dev/null
+++ b/backend/UniVerse.Application/Interfaces/IAchievementService.cs
@@ -0,0 +1,12 @@
+using UniVerse.Application.DTOs.Achievements;
+
+namespace UniVerse.Application.Interfaces;
+
+public interface IAchievementService
+{
+    Task<List<AchievementDto>> GetAllAsync();
+    Task<AchievementDto> GetByIdAsync(int id);
+    Task<AchievementDto> CreateAsync(CreateAchievementRequest request);
+    Task<AchievementDto> UpdateAsync(int id, UpdateAchievementRequest request);
+    Task DeleteAsync(int id);
+}
diff --git a/backend/UniVerse.Application/Interfaces/IAuthService.cs b/backend/UniVerse.Application/Interfaces/IAuthService.cs
new file mode 100644
index 0000000..26a8b4c
--- /dev/null
+++ b/backend/UniVerse.Application/Interfaces/IAuthService.cs
@@ -0,0 +1,13 @@
+using UniVerse.Application.DTOs.Auth;
+using UniVerse.Application.DTOs.Users;
+
+namespace UniVerse.Application.Interfaces;
+
+public interface IAuthService
+{
+    Task<AuthResponse> LoginWithMicrosoftAsync(string authorizationCode);
+    Task<AuthResponse> DevLoginAsync(string email, string? displayName, Domain.Enums.UserRole role);
+    Task<AuthResponse> RefreshTokenAsync(string refreshToken);
+    Task RevokeRefreshTokenAsync(string refreshToken);
+    Task<UserDto> GetCurrentUserAsync(int userId);
+}
diff --git a/backend/UniVerse.Application/Interfaces/ICourseService.cs b/backend/UniVerse.Application/Interfaces/ICourseService.cs
new file mode 100644
index 0000000..62710fc
--- /dev/null
+++ b/backend/UniVerse.Application/Interfaces/ICourseService.cs
@@ -0,0 +1,15 @@
+using UniVerse.Application.DTOs.Common;
+using UniVerse.Application.DTOs.Courses;
+
+namespace UniVerse.Application.Interfaces;
+
+public interface ICourseService
+{
+    Task<PagedResult<CourseDto>> GetAllAsync(CourseFilterRequest filter);
+    Task<CourseDto> GetByIdAsync(int id);
+    Task<CourseDto> CreateAsync(CreateCourseRequest request);
+    Task<CourseDto> UpdateAsync(int id, UpdateCourseRequest request);
+    Task DeleteAsync(int id);
+    Task AddTagAsync(int courseId, int tagId);
+    Task RemoveTagAsync(int courseId, int tagId);
+}
diff --git a/backend/UniVerse.Application/Interfaces/IGamificationService.cs b/backend/UniVerse.Application/Interfaces/IGamificationService.cs
new file mode 100644
index 0000000..387b60c
--- /dev/null
+++ b/backend/UniVerse.Application/Interfaces/IGamificationService.cs
@@ -0,0 +1,16 @@
+using UniVerse.Application.DTOs.Achievements;
+using UniVerse.Application.DTOs.Common;
+using UniVerse.Application.DTOs.Gamification;
+using UniVerse.Domain.Enums;
+
+namespace UniVerse.Application.Interfaces;
+
+public interface IGamificationService
+{
+    Task AwardCoinsAsync(int userId, int amount, CoinTransactionType type,
+        int? reviewId = null, int? achievementId = null, string? description = null);
+    Task CheckAndAwardAchievementsAsync(int userId);
+    int CalculateLevel(int xp);
+    Task<List<UserAchievementDto>> GetUserAchievementsAsync(int userId);
+    Task<PagedResult<CoinTransactionDto>> GetTransactionsAsync(int userId, PaginationRequest pagination);
+}
diff --git a/backend/UniVerse.Application/Interfaces/ILectureService.cs b/backend/UniVerse.Application/Interfaces/ILectureService.cs
new file mode 100644
index 0000000..2dd11ad
--- /dev/null
+++ b/backend/UniVerse.Application/Interfaces/ILectureService.cs
@@ -0,0 +1,17 @@
+using UniVerse.Application.DTOs.Common;
+using UniVerse.Application.DTOs.Lectures;
+
+namespace UniVerse.Application.Interfaces;
+
+public interface ILectureService
+{
+    Task<PagedResult<LectureDto>> GetAllAsync(LectureFilterRequest filter);
+    Task<LectureDetailDto> GetByIdAsync(int id, int? currentUserId = null);
+    Task<LectureDto> CreateAsync(CreateLectureRequest request);
+    Task<LectureDto> UpdateAsync(int id, UpdateLectureRequest request);
+    Task DeleteAsync(int id);
+    Task EnrollAsync(int lectureId, int userId);
+    Task UnenrollAsync(int lectureId, int userId);
+    Task MarkAttendanceAsync(int lectureId, int userId, bool attended);
+    Task<PagedResult<EnrollmentDto>> GetEnrollmentsAsync(int lectureId, PaginationRequest pagination);
+}
diff --git a/backend/UniVerse.Application/Interfaces/ILlmAnalysisService.cs b/backend/UniVerse.Application/Interfaces/ILlmAnalysisService.cs
new file mode 100644
index 0000000..7f5af0a
--- /dev/null
+++ b/backend/UniVerse.Application/Interfaces/ILlmAnalysisService.cs
@@ -0,0 +1,7 @@
+namespace UniVerse.Application.Interfaces;
+
+public interface ILlmAnalysisService
+{
+    Task AnalyzeReviewAsync(int reviewId);
+    Task ProcessPendingReviewsAsync();
+}
diff --git a/backend/UniVerse.Application/Interfaces/ILlmClient.cs b/backend/UniVerse.Application/Interfaces/ILlmClient.cs
new file mode 100644
index 0000000..dccefda
--- /dev/null
+++ b/backend/UniVerse.Application/Interfaces/ILlmClient.cs
@@ -0,0 +1,13 @@
+namespace UniVerse.Application.Interfaces;
+
+public record LlmReviewAnalysis(
+    double QualityScore,
+    string Sentiment,
+    string[] Tags,
+    bool IsInformative
+);
+
+public interface ILlmClient
+{
+    Task<LlmReviewAnalysis> AnalyzeReviewAsync(string reviewText, string lectureContext);
+}
diff --git a/backend/UniVerse.Application/Interfaces/ILocationService.cs b/backend/UniVerse.Application/Interfaces/ILocationService.cs
new file mode 100644
index 0000000..1487088
--- /dev/null
+++ b/backend/UniVerse.Application/Interfaces/ILocationService.cs
@@ -0,0 +1,12 @@
+using UniVerse.Application.DTOs.Locations;
+
+namespace UniVerse.Application.Interfaces;
+
+public interface ILocationService
+{
+    Task<List<LocationDto>> GetAllAsync();
+    Task<LocationDto> GetByIdAsync(int id);
+    Task<LocationDto> CreateAsync(CreateLocationRequest request);
+    Task<LocationDto> UpdateAsync(int id, UpdateLocationRequest request);
+    Task DeleteAsync(int id);
+}
diff --git a/backend/UniVerse.Application/Interfaces/IReviewService.cs b/backend/UniVerse.Application/Interfaces/IReviewService.cs
new file mode 100644
index 0000000..8d3330a
--- /dev/null
+++ b/backend/UniVerse.Application/Interfaces/IReviewService.cs
@@ -0,0 +1,16 @@
+using UniVerse.Application.DTOs.Common;
+using UniVerse.Application.DTOs.Reviews;
+
+namespace UniVerse.Application.Interfaces;
+
+public interface IReviewService
+{
+    Task<ReviewDto> CreateAsync(int userId, CreateReviewRequest request);
+    Task<ReviewDto> GetByIdAsync(int id);
+    Task<ReviewDto> UpdateAsync(int id, int userId, UpdateReviewRequest request);
+    Task DeleteAsync(int id, int userId, bool isAdmin = false);
+    Task<PagedResult<ReviewDto>> GetByLectureAsync(int lectureId, PaginationRequest pagination);
+    Task<PagedResult<ReviewDto>> GetByUserAsync(int userId, PaginationRequest pagination);
+    Task<PagedResult<ReviewDto>> GetPendingAsync(PaginationRequest pagination);
+    Task ReanalyzeAsync(int id);
+}
diff --git a/backend/UniVerse.Application/Interfaces/IScheduleSyncService.cs b/backend/UniVerse.Application/Interfaces/IScheduleSyncService.cs
new file mode 100644
index 0000000..7558af7
--- /dev/null
+++ b/backend/UniVerse.Application/Interfaces/IScheduleSyncService.cs
@@ -0,0 +1,25 @@
+using UniVerse.Application.DTOs.Sync;
+
+namespace UniVerse.Application.Interfaces;
+
+public interface IScheduleSyncService
+{
+    Task<SyncResultDto> SyncScheduleAsync(SyncScheduleRequest request);
+    Task<SyncResultDto> SyncRoomsAsync();
+    Task<List<EmployeeDto>> SearchEmployeesAsync(string fullname);
+    Task<SyncStatusDto> GetLastSyncStatusAsync();
+}
+
+public interface IModeusApiClient
+{
+    Task<ModeusEventsResponse> SearchEventsAsync(SyncScheduleRequest request);
+    Task<ModeusRoomsResponse> SearchRoomsAsync();
+    Task<List<ModeusEmployee>> SearchEmployeeAsync(string fullname);
+}
+
+// Modeus API response models
+public record ModeusEvent(string Id, string Name, DateTime StartsAt, DateTime EndsAt, string? RoomId, string? TeacherId, string? TypeId);
+public record ModeusEventsResponse(List<ModeusEvent> Events);
+public record ModeusRoom(string Id, string Name, string? Building);
+public record ModeusRoomsResponse(List<ModeusRoom> Rooms);
+public record ModeusEmployee(string? Id, string FullName, string? Department);
diff --git a/backend/UniVerse.Application/Interfaces/ITagService.cs b/backend/UniVerse.Application/Interfaces/ITagService.cs
new file mode 100644
index 0000000..e492dcc
--- /dev/null
+++ b/backend/UniVerse.Application/Interfaces/ITagService.cs
@@ -0,0 +1,15 @@
+using UniVerse.Application.DTOs.Common;
+using UniVerse.Application.DTOs.Tags;
+using UniVerse.Domain.Enums;
+
+namespace UniVerse.Application.Interfaces;
+
+public interface ITagService
+{
+    Task<List<TagDto>> GetAllAsync(TagType? type = null, int? parentId = null);
+    Task<TagDto> GetByIdAsync(int id);
+    Task<TagDto> CreateAsync(CreateTagRequest request);
+    Task<TagDto> UpdateAsync(int id, UpdateTagRequest request);
+    Task DeleteAsync(int id);
+    Task<List<TagTreeDto>> GetTreeAsync();
+}
diff --git a/backend/UniVerse.Application/Interfaces/IUserService.cs b/backend/UniVerse.Application/Interfaces/IUserService.cs
new file mode 100644
index 0000000..4625450
--- /dev/null
+++ b/backend/UniVerse.Application/Interfaces/IUserService.cs
@@ -0,0 +1,15 @@
+using UniVerse.Application.DTOs.Common;
+using UniVerse.Application.DTOs.Users;
+using UniVerse.Domain.Enums;
+
+namespace UniVerse.Application.Interfaces;
+
+public interface IUserService
+{
+    Task<UserDto> GetByIdAsync(int id);
+    Task<UserDto> UpdateProfileAsync(int id, UpdateUserRequest request);
+    Task<UserStatsDto> GetStatsAsync(int id);
+    Task<PagedResult<UserDto>> GetAllAsync(UserFilterRequest filter);
+    Task SetRoleAsync(int id, UserRole role);
+    Task SetActiveAsync(int id, bool isActive);
+}
diff --git a/backend/UniVerse.Application/Mappings/MappingExtensions.cs b/backend/UniVerse.Application/Mappings/MappingExtensions.cs
new file mode 100644
index 0000000..a332e41
--- /dev/null
+++ b/backend/UniVerse.Application/Mappings/MappingExtensions.cs
@@ -0,0 +1,98 @@
+using UniVerse.Application.DTOs.Achievements;
+using UniVerse.Application.DTOs.Auth;
+using UniVerse.Application.DTOs.Courses;
+using UniVerse.Application.DTOs.Gamification;
+using UniVerse.Application.DTOs.Lectures;
+using UniVerse.Application.DTOs.Locations;
+using UniVerse.Application.DTOs.Reviews;
+using UniVerse.Application.DTOs.Tags;
+using UniVerse.Application.DTOs.Users;
+using UniVerse.Domain.Entities;
+
+namespace UniVerse.Application.Mappings;
+
+public static class MappingExtensions
+{
+    // --- User ---
+    public static UserDto ToDto(this User user, int level) => new(
+        user.Id, user.Email, user.DisplayName, user.AvatarUrl,
+        user.Role, user.IsActive, user.Xp, user.Coins, level, user.CreatedAt
+    );
+
+    public static UserAuthDto ToAuthDto(this User user) => new(
+        user.Id, user.Email, user.DisplayName, user.Role
+    );
+
+    // --- Tag ---
+    public static TagDto ToDto(this Tag tag) => new(
+        tag.Id, tag.Name, tag.Type, tag.ParentId, tag.CreatedAt
+    );
+
+    public static TagTreeDto ToTreeDto(this Tag tag) => new(
+        tag.Id, tag.Name, tag.Type,
+        tag.Children.Select(c => c.ToTreeDto()).ToList()
+    );
+
+    // --- Location ---
+    public static LocationDto ToDto(this Location loc) => new(
+        loc.Id, loc.Name, loc.Building, loc.Room, loc.Address, loc.CreatedAt
+    );
+
+    // --- Course ---
+    public static CourseDto ToDto(this Course course) => new(
+        course.Id, course.Name, course.Description, course.IsSynced,
+        course.CourseTags.Select(ct => ct.Tag.ToDto()).ToList(),
+        course.CreatedAt
+    );
+
+    // --- Lecture ---
+    public static LectureDto ToDto(this Lecture lecture) => new(
+        lecture.Id, lecture.CourseId, lecture.Course?.Name ?? "",
+        lecture.TeacherId, lecture.Teacher?.DisplayName,
+        lecture.LocationId, lecture.Location?.Name,
+        lecture.Title, lecture.Description, lecture.Format,
+        lecture.StartsAt, lecture.EndsAt, lecture.IsOpen,
+        lecture.MaxEnrollments, lecture.Enrollments.Count,
+        lecture.OnlineUrl, lecture.CreatedAt
+    );
+
+    public static LectureDetailDto ToDetailDto(this Lecture lecture, bool isEnrolled) => new(
+        lecture.Id, lecture.CourseId, lecture.Course?.Name ?? "",
+        lecture.TeacherId, lecture.Teacher?.DisplayName,
+        lecture.LocationId, lecture.Location?.Name,
+        lecture.Title, lecture.Description, lecture.Format,
+        lecture.StartsAt, lecture.EndsAt, lecture.IsOpen,
+        lecture.MaxEnrollments, lecture.Enrollments.Count,
+        lecture.OnlineUrl, lecture.CreatedAt, isEnrolled
+    );
+
+    // --- Enrollment ---
+    public static EnrollmentDto ToDto(this LectureEnrollment enrollment) => new(
+        enrollment.Id, enrollment.UserId,
+        enrollment.User?.DisplayName, enrollment.User?.Email,
+        enrollment.Attended, enrollment.CreatedAt
+    );
+
+    // --- Review ---
+    public static ReviewDto ToDto(this Review review) => new(
+        review.Id, review.LectureId, review.Lecture?.Title,
+        review.UserId, review.User?.DisplayName,
+        review.Rating, review.Text, review.LlmStatus,
+        review.Sentiment, review.QualityScore, review.IsInformative,
+        review.LlmTags, review.CreatedAt
+    );
+
+    // --- Achievement ---
+    public static AchievementDto ToDto(this Achievement a) => new(
+        a.Id, a.Name, a.Description, a.IconUrl, a.XpReward, a.CoinReward, a.Condition, a.CreatedAt
+    );
+
+    public static UserAchievementDto ToDto(this UserAchievement ua) => new(
+        ua.Id, ua.Achievement.ToDto(), ua.AwardedAt
+    );
+
+    // --- CoinTransaction ---
+    public static CoinTransactionDto ToDto(this CoinTransaction ct) => new(
+        ct.Id, ct.Amount, ct.Type, ct.ReviewId, ct.AchievementId, ct.Description, ct.CreatedAt
+    );
+}
diff --git a/backend/UniVerse.Application/UniVerse.Application.csproj b/backend/UniVerse.Application/UniVerse.Application.csproj
new file mode 100644
index 0000000..d83e800
--- /dev/null
+++ b/backend/UniVerse.Application/UniVerse.Application.csproj
@@ -0,0 +1,23 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+    <PropertyGroup>
+        <TargetFramework>net10.0</TargetFramework>
+        <Nullable>enable</Nullable>
+        <ImplicitUsings>enable</ImplicitUsings>
+        <RootNamespace>UniVerse.Application</RootNamespace>
+    </PropertyGroup>
+
+    <ItemGroup>
+        <PackageReference Include="FluentValidation.DependencyInjectionExtensions" Version="12.0.0" />
+        <PackageReference Include="Microsoft.Extensions.Configuration.Abstractions" Version="10.0.0" />
+        <PackageReference Include="Microsoft.Extensions.Logging.Abstractions" Version="10.0.0" />
+        <PackageReference Include="System.IdentityModel.Tokens.Jwt" Version="8.7.0" />
+        <PackageReference Include="Microsoft.IdentityModel.Tokens" Version="8.7.0" />
+        <PackageReference Include="Microsoft.EntityFrameworkCore" Version="10.0.0" />
+    </ItemGroup>
+
+    <ItemGroup>
+        <ProjectReference Include="..\UniVerse.Domain\UniVerse.Domain.csproj" />
+    </ItemGroup>
+
+</Project>