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/pages/GalleryPage.tsx

@@ -13,6 +13,7 @@ import { GalleryView } from '../components/gallery';
 import { analyticsService } from '../services/analytics.service';
 import { api } from '../config/api';
 import { GALLERY_THEME_PRESETS } from '../types/theme.types';
+import { buildResourceUrl } from '../utils/url';
 
 export const GalleryPage: React.FC = () => {
   const { slug, token } = useParams<{ slug: string; token?: string }>();
@@ -164,7 +165,7 @@ export const GalleryPage: React.FC = () => {
           {settingsData?.branding_logo_url && (
             <div className="p-8 text-center">
               <img 
-                src={`${import.meta.env.VITE_API_URL || 'http://localhost:3001'}${settingsData.branding_logo_url}`} 
+                src={buildResourceUrl(settingsData.branding_logo_url)} 
                 alt={settingsData.branding_company_name || 'Company Logo'}
                 className="h-16 w-auto object-contain mx-auto"
               />
@@ -220,7 +221,7 @@ export const GalleryPage: React.FC = () => {
           {settingsData?.branding_logo_url && (
             <div className="p-8 text-center">
               <img 
-                src={`${import.meta.env.VITE_API_URL || 'http://localhost:3001'}${settingsData.branding_logo_url}`} 
+                src={buildResourceUrl(settingsData.branding_logo_url)} 
                 alt={settingsData.branding_company_name || 'Company Logo'}
                 className="h-16 w-auto object-contain mx-auto"
               />
@@ -282,7 +283,7 @@ export const GalleryPage: React.FC = () => {
           <div className="text-center mb-4 sm:mb-6">
             <img 
               src={settingsData?.branding_logo_url ? 
-                `${import.meta.env.VITE_API_URL || 'http://localhost:3001'}${settingsData.branding_logo_url}` : 
+                buildResourceUrl(settingsData.branding_logo_url) : 
                 '/picpeak-logo-transparent.png'
               } 
               alt={settingsData?.branding_company_name || 'PicPeak'}