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/nginx.conf

@@ -79,6 +79,20 @@ server {
         proxy_cache_valid 404 1m;
     }
 
+    # Uploads serving proxy (logos, favicons, watermarks)
+    location /uploads {
+        proxy_pass http://backend:3000;
+        proxy_http_version 1.1;
+        proxy_set_header Host $host;
+        proxy_set_header X-Real-IP $remote_addr;
+        proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
+        proxy_set_header X-Forwarded-Proto $scheme;
+        
+        # Cache uploads
+        proxy_cache_valid 200 302 7d;
+        proxy_cache_valid 404 1m;
+    }
+
     # SPA fallback
     location / {
         try_files $uri $uri/ /index.html;