fix: resolve branding display issues and invitation parsing errors

Fixes #84 - Logo and favicon not displaying on branding page and galleries
Fixes #85 - Invitations showing undefined expiresAt causing parseISO errors

Changes:
- Fix nginx.conf: Add ^~ modifier to /uploads location to prioritize proxy over static file matching
- Fix vite.config.ts: Add /uploads proxy for development environment
- Fix BrandingPage.tsx: Include logo_url from branding settings instead of expecting it from theme
- Fix adminUsers.js: Add transformInvitation() to convert snake_case DB fields to camelCase API response
- Fix publicSettings.js: Add branding_hide_powered_by to public settings API response
- Update README.md: Mark Multiple Administrators feature as implemented
- Bump version to 2.2.1

frontend/nginx.conf

@@ -88,7 +88,8 @@ server {
     }
 
     # Uploads serving proxy (logos, favicons, watermarks)
-    location /uploads {
+    # ^~ modifier stops regex matching, ensuring uploads are proxied not served locally
+    location ^~ /uploads {
         proxy_pass http://backend:3001;
         proxy_http_version 1.1;
         proxy_set_header Host $host;