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/auth/guards/auth.guard.ts

@@ -6,13 +6,13 @@ import {
 } from "@nestjs/common";
 import { ConfigService } from "@nestjs/config";
 import { getIronSession } from "iron-session";
-import { CryptoService } from "../../crypto/crypto.service";
+import { JwtService } from "../../crypto/services/jwt.service";
 import { getSessionOptions, SessionData } from "../session.config";
 
 @Injectable()
 export class AuthGuard implements CanActivate {
 	constructor(
-		private readonly cryptoService: CryptoService,
+		private readonly jwtService: JwtService,
 		private readonly configService: ConfigService,
 	) {}
 
@@ -33,7 +33,7 @@ export class AuthGuard implements CanActivate {
 		}
 
 		try {
-			const payload = await this.cryptoService.verifyJwt(token);
+			const payload = await this.jwtService.verifyJwt(token);
 			request.user = payload;
 		} catch {
 			throw new UnauthorizedException();