feat: include user role in JWT payload

- Updated `request.interface.ts` to add `role` to the user object.
- Modified `auth.service.ts` to include `role` in the JWT payload.

backend/src/common/interfaces/request.interface.ts

@@ -4,5 +4,6 @@ export interface AuthenticatedRequest extends Request {
 	user: {
 		sub: string;
 		username: string;
+		role: string;
 	};
 }