Fix admin login and CORS issues

- Update CORS configuration to allow frontend on port 3005
- Fix auth service to map email field to username for backend compatibility
- Add loading state handling in AdminLayout
- Add error boundary to dashboard route
- Fix unused parameter warning in login function

🤖 Generated with [Claude Code](https://claude.ai/code)

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

backend/server.js

@@ -21,7 +21,7 @@ const PORT = process.env.PORT || 3000;
 // Security middleware
 app.use(helmet());
 app.use(cors({
-  origin: process.env.FRONTEND_URL || 'http://localhost:3001',
+  origin: process.env.FRONTEND_URL || 'http://localhost:3005',
   credentials: true
 }));