feat: implement AuthModule with authentication and RBAC features

Added AuthModule with services, controllers, and guards for authentication. Implements session management, role-based access control, 2FA, and DTOs for user login, registration, and token refresh.

backend/src/auth/decorators/roles.decorator.ts

@@ -0,0 +1,3 @@
+import { SetMetadata } from "@nestjs/common";
+
+export const Roles = (...roles: string[]) => SetMetadata("roles", roles);