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/components/MaintenanceMode.tsx

@@ -3,6 +3,7 @@ import { AlertTriangle } from 'lucide-react';
 import { useQuery } from '@tanstack/react-query';
 import { useTranslation } from 'react-i18next';
 import { api } from '../config/api';
+import { buildResourceUrl } from '../utils/url';
 
 interface BrandingSettings {
   branding_company_name?: string;
@@ -50,7 +51,7 @@ export const MaintenanceMode: React.FC = () => {
               src={settings?.branding_logo_url ? 
                 (settings.branding_logo_url.startsWith('http') 
                   ? settings.branding_logo_url 
-                  : `${import.meta.env.VITE_API_URL || 'http://localhost:3001'}${settings.branding_logo_url}`)
+                  : buildResourceUrl(settings.branding_logo_url))
                 : '/picpeak-logo-transparent.png'
               } 
               alt={settings?.branding_company_name || 'PicPeak'}