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/pages/admin/SettingsPage.tsx

@@ -1,20 +1,16 @@
 import React, { useState } from 'react';
 import { 
   Save, 
-  Shield, 
-  HardDrive, 
-  Bell,
   Database,
   Globe,
   Key,
-  AlertCircle,
-  CheckCircle
+  AlertCircle
 } from 'lucide-react';
 import { toast } from 'react-toastify';
 
 import { Button, Card, Input, Loading } from '../../components/common';
 import { useQuery, useMutation, useQueryClient } from '@tanstack/react-query';
-import { settingsService, type BrandingSettings, type ThemeSettings, type StorageInfo } from '../../services/settings.service';
+import { settingsService } from '../../services/settings.service';
 
 export const SettingsPage: React.FC = () => {
   const [activeTab, setActiveTab] = useState<'general' | 'storage' | 'security'>('general');