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>

frontend/src/components/admin/AdminSidebar.tsx

@@ -40,7 +40,7 @@ export const AdminSidebar: React.FC<AdminSidebarProps> = ({ isOpen, onClose }) =
 
   return (
     <div
-      className={`fixed inset-y-0 left-0 z-50 w-64 bg-white border-r border-neutral-200 transform transition-transform duration-200 ease-in-out lg:translate-x-0 lg:static ${
+      className={`fixed inset-y-0 left-0 z-50 w-64 bg-white border-r border-neutral-200 transform transition-transform duration-200 ease-in-out lg:relative lg:translate-x-0 ${
         isOpen ? 'translate-x-0' : '-translate-x-full'
       }`}
     >
@@ -87,7 +87,6 @@ export const AdminSidebar: React.FC<AdminSidebarProps> = ({ isOpen, onClose }) =
 
         {/* Storage Info */}
         <StorageInfo />
-        </div>
       </div>
     </div>
   );