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/contents/contents.module.ts

@@ -6,10 +6,11 @@ import { MediaModule } from "../media/media.module";
 import { S3Module } from "../s3/s3.module";
 import { ContentsController } from "./contents.controller";
 import { ContentsService } from "./contents.service";
+import { ContentsRepository } from "./repositories/contents.repository";
 
 @Module({
 	imports: [DatabaseModule, S3Module, AuthModule, CryptoModule, MediaModule],
 	controllers: [ContentsController],
-	providers: [ContentsService],
+	providers: [ContentsService, ContentsRepository],
 })
 export class ContentsModule {}