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/AdminLayout.tsx

@@ -25,7 +25,7 @@ export const AdminLayout: React.FC = () => {
   }
 
   return (
-    <div className="min-h-screen bg-neutral-50">
+    <div className="min-h-screen bg-neutral-50 flex">
       {/* Mobile sidebar backdrop */}
       {sidebarOpen && (
         <div
@@ -38,12 +38,12 @@ export const AdminLayout: React.FC = () => {
       <AdminSidebar isOpen={sidebarOpen} onClose={() => setSidebarOpen(false)} />
 
       {/* Main content */}
-      <div className="lg:pl-64">
+      <div className="flex-1 flex flex-col min-w-0">
         {/* Header */}
         <AdminHeader onMenuClick={() => setSidebarOpen(true)} />
 
         {/* Page content */}
-        <main id="main-content" className="px-4 sm:px-6 lg:px-8 py-8">
+        <main id="main-content" className="flex-1 px-4 sm:px-6 lg:px-8 py-8">
           <Outlet />
         </main>
       </div>