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/media/media.service.spec.ts

@@ -6,6 +6,9 @@ import ffmpeg from "fluent-ffmpeg";
 import sharp from "sharp";
 import { MediaService } from "./media.service";
 
+import { ImageProcessorStrategy } from "./strategies/image-processor.strategy";
+import { VideoProcessorStrategy } from "./strategies/video-processor.strategy";
+
 jest.mock("sharp");
 jest.mock("fluent-ffmpeg");
 jest.mock("node:fs/promises");
@@ -29,6 +32,8 @@ describe("MediaService", () => {
 		const module: TestingModule = await Test.createTestingModule({
 			providers: [
 				MediaService,
+				ImageProcessorStrategy,
+				VideoProcessorStrategy,
 				{
 					provide: ConfigService,
 					useValue: {