fix: add explicit Router type annotation to resolve TS2742 build error

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: sai-aarna

apps/api/src/routes/admin.routes.ts

@@ -3,7 +3,7 @@ import { adminAuthMiddleware } from '../middleware/adminAuth.middleware';
 import * as admin from '../handlers/admin.handler';
 import { adminLogin } from '../handlers/adminLogin.handler';
 
-export const adminRouter = Router();
+export const adminRouter: Router = Router();
 
 // Login is unauthenticated — it issues the session token
 adminRouter.post('/login', adminLogin);