fix: remove hardcoded localhost URLs for production deployment

- Add URL utility functions for building resource URLs
- Update all components to use relative URLs in production
- Add production deployment documentation
- Update nginx config to proxy all required endpoints
- Add .env.production.example with proper configuration

frontend/src/App.tsx

@@ -27,6 +27,7 @@ import { AdminLayout, AdminAuthWrapper } from './components/admin';
 import { PageErrorBoundary, OfflineIndicator, SkipLink, DynamicFavicon } from './components/common';
 import { MaintenanceWrapper } from './components/MaintenanceWrapper';
 import { GlobalThemeProvider } from './components/GlobalThemeProvider';
+import { getApiBaseUrl } from './utils/url';
 
 // Create a client
 const queryClient = new QueryClient({
@@ -48,7 +49,7 @@ function App() {
       if (umamiUrl && umamiWebsiteId) {
         try {
           // Fetch public settings to check if analytics is enabled
-          const response = await fetch(`${import.meta.env.VITE_API_URL || 'http://localhost:3001'}/api/public/settings`);
+          const response = await fetch(`${getApiBaseUrl()}/public/settings`);
           const settings = await response.json();
           
           // Only initialize if analytics is enabled in settings