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>

frontend/src/components/admin/AdminLayout.tsx

@@ -6,9 +6,20 @@ import { AdminSidebar } from './AdminSidebar';
 import { AdminHeader } from './AdminHeader';
 
 export const AdminLayout: React.FC = () => {
-  const { isAuthenticated } = useAdminAuth();
+  const { isAuthenticated, isLoading } = useAdminAuth();
   const [sidebarOpen, setSidebarOpen] = useState(false);
 
+  if (isLoading) {
+    return (
+      <div className="min-h-screen bg-neutral-50 flex items-center justify-center">
+        <div className="text-center">
+          <div className="w-16 h-16 border-4 border-primary-600 border-t-transparent rounded-full animate-spin mx-auto mb-4"></div>
+          <p className="text-neutral-600">Loading...</p>
+        </div>
+      </div>
+    );
+  }
+
   if (!isAuthenticated) {
     return <Navigate to="/admin/login" replace />;
   }