Fix admin interface issues and 404 errors

- Create adminEvents.js router to handle /api/admin/events endpoints
- Mount events router in admin.js to fix 404 errors
- Fix admin layout CSS - changed from static to flex layout
- Update AdminSidebar positioning from static to relative
- Add missing PUT endpoints for general and security settings
- Fix frontend environment variables in docker-compose.local.yml
- Add build args to Dockerfile.dev for environment variables
- Update CORS to accept requests from all dev servers
- Remove unused imports from SettingsPage

This fixes:
- Events page 404 error
- Admin layout misalignment (sidebar and content on different rows)
- Settings page not loading
- CORS issues between frontend and backend

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

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

backend/server.js

@@ -20,10 +20,29 @@ const PORT = process.env.PORT || 3000;
 
 // Security middleware
 app.use(helmet());
-app.use(cors({
-  origin: process.env.FRONTEND_URL || 'http://localhost:3005',
+
+// CORS configuration
+const corsOptions = {
+  origin: function (origin, callback) {
+    const allowedOrigins = [
+      process.env.FRONTEND_URL || 'http://localhost:3005',
+      process.env.ADMIN_URL || 'http://localhost:3005',
+      'http://localhost:3002', // Vite dev server
+      'http://localhost:3001', // For API testing
+      'http://localhost:3000'  // Direct backend access
+    ];
+    
+    // Allow requests with no origin (like mobile apps or curl)
+    if (!origin || allowedOrigins.indexOf(origin) !== -1) {
+      callback(null, true);
+    } else {
+      callback(new Error('Not allowed by CORS'));
+    }
+  },
   credentials: true
-}));
+};
+
+app.use(cors(corsOptions));
 
 // Rate limiting
 const limiter = rateLimit({