feat: add modular services and repositories for improved code organization

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.

backend/src/users/users.module.ts

@@ -4,11 +4,12 @@ import { CryptoModule } from "../crypto/crypto.module";
 import { DatabaseModule } from "../database/database.module";
 import { UsersController } from "./users.controller";
 import { UsersService } from "./users.service";
+import { UsersRepository } from "./repositories/users.repository";
 
 @Module({
 	imports: [DatabaseModule, CryptoModule, AuthModule],
 	controllers: [UsersController],
-	providers: [UsersService],
+	providers: [UsersService, UsersRepository],
 	exports: [UsersService],
 })
 export class UsersModule {}