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/App.tsx

@@ -20,7 +20,7 @@ import {
   BrandingPage
 } from './pages/admin';
 import { AdminLayout } from './components/admin';
-import { PageErrorBoundary, OfflineIndicator, SkipLink } from './components/common';
+import { PageErrorBoundary, ErrorBoundary, OfflineIndicator, SkipLink } from './components/common';
 
 // Create a client
 const queryClient = new QueryClient({
@@ -68,7 +68,7 @@ function App() {
                 <Routes>
                   <Route path="login" element={<AdminLoginPage />} />
                   <Route element={<AdminLayout />}>
-                    <Route path="dashboard" element={<AdminDashboard />} />
+                    <Route path="dashboard" element={<ErrorBoundary><AdminDashboard /></ErrorBoundary>} />
                     <Route path="events" element={<EventsListPage />} />
                     <Route path="events/new" element={<CreateEventPage />} />
                     <Route path="events/:id" element={<EventDetailsPage />} />