Introduce repository pattern across multiple services, including `favorites`, `tags`, `sessions`, `reports`, `auth`, and more. Decouple crypto functionalities into modular services like `HashingService`, `JwtService`, and `EncryptionService`. Improve testability and maintainability by simplifying dependencies and consolidating utility logic.
Added AuthModule with services, controllers, and guards for authentication. Implements session management, role-based access control, 2FA, and DTOs for user login, registration, and token refresh.
