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/api-keys/api-keys.module.ts

@@ -4,11 +4,12 @@ import { CryptoModule } from "../crypto/crypto.module";
 import { DatabaseModule } from "../database/database.module";
 import { ApiKeysController } from "./api-keys.controller";
 import { ApiKeysService } from "./api-keys.service";
+import { ApiKeysRepository } from "./repositories/api-keys.repository";
 
 @Module({
 	imports: [DatabaseModule, AuthModule, CryptoModule],
 	controllers: [ApiKeysController],
-	providers: [ApiKeysService],
+	providers: [ApiKeysService, ApiKeysRepository],
 	exports: [ApiKeysService],
 })
 export class ApiKeysModule {}