fix: resolve frontend API routing issues for Traefik deployment

Major fixes for production deployment with Traefik:

1. API Path Fixes:
   - Remove double /api prefix from all frontend service calls
   - Fix auth.service.ts to use correct paths (/auth/admin/login)
   - Update all services to use single /api prefix from base URL
   - Fix template literal paths in photo services

2. Docker Configuration:
   - Add build args for VITE_API_URL in docker-compose.prod.yml
   - Create Dockerfile.prod with proper API URL configuration
   - Ensure frontend is built with correct API base path

3. Documentation:
   - Add comprehensive TRAEFIK_DEPLOYMENT.md guide
   - Document proper Traefik labels and routing configuration
   - Include troubleshooting steps for common issues
   - Explain network configuration and SSL handling

This resolves:
- 502 Bad Gateway errors
- Double /api/api paths in requests
- Frontend unable to communicate with backend
- Login functionality not working

The frontend now correctly calls the backend API through Traefik's
routing, with all requests going to /api/* being forwarded to the
backend service on port 3000.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

frontend/src/components/gallery/UserPhotoUpload.tsx

@@ -63,7 +63,7 @@ export const UserPhotoUpload: React.FC<UserPhotoUploadProps> = ({
       }
 
       try {
-        await api.post(`/api/gallery/${eventId}/upload`, formData, {
+        await api.post(`/gallery/${eventId}/upload`, formData, {
           headers: {
             'Content-Type': 'multipart/form-data',
           },