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/common/DynamicFavicon.tsx

@@ -1,12 +1,13 @@
 import { useEffect } from 'react';
 import { useQuery } from '@tanstack/react-query';
+import { getApiBaseUrl, buildResourceUrl } from '../../utils/url';
 
 export const DynamicFavicon: React.FC = () => {
   const { data: settings } = useQuery({
     queryKey: ['public-settings'],
     queryFn: async () => {
       try {
-        const response = await fetch(`${import.meta.env.VITE_API_URL || 'http://localhost:3001'}/api/public/settings`);
+        const response = await fetch(`${getApiBaseUrl()}/public/settings`);
         if (response.ok) {
           return response.json();
         }
@@ -30,7 +31,7 @@ export const DynamicFavicon: React.FC = () => {
       link.type = 'image/png';
       link.href = settings.branding_favicon_url.startsWith('http') 
         ? settings.branding_favicon_url 
-        : `${import.meta.env.VITE_API_URL || 'http://localhost:3001'}${settings.branding_favicon_url}`;
+        : buildResourceUrl(settings.branding_favicon_url);
       
       document.head.appendChild(link);
     }