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 CryptoModule providing services for Argon2 hashing, JWT handling, JWE encryption/decryption, JWS signing/verification, and post-quantum cryptography (ML-KEM). Includes extensive unit tests for all features.
