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/ReCaptcha.tsx

@@ -1,6 +1,7 @@
 import React, { useEffect, useState } from 'react';
 import ReCAPTCHA from 'react-google-recaptcha';
 import { useQuery } from '@tanstack/react-query';
+import { getApiBaseUrl } from '../../utils/url';
 
 interface ReCaptchaProps {
   onChange: (token: string | null) => void;
@@ -20,7 +21,7 @@ export const ReCaptcha: React.FC<ReCaptchaProps> = ({
   const { data: settings } = useQuery({
     queryKey: ['public-settings'],
     queryFn: async () => {
-      const response = await fetch(`${import.meta.env.VITE_API_URL || 'http://localhost:3001'}/api/public/settings`);
+      const response = await fetch(`${getApiBaseUrl()}/public/settings`);
       return response.json();
     },
     staleTime: 5 * 60 * 1000, // Cache for 5 minutes