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

README.md

@@ -248,7 +248,7 @@ These features are currently in beta testing and may have limited functionality
 | **Face Recognition** | AI-powered face detection to help guests find their photos and create automatic person-based albums | Low | 🔄 Open |
 | **Gallery Feedback** | Allow guests to like, rate, and comment on photos with admin notifications and moderation | Medium | ✅ Implemented |
 | **Video Support** | Upload and display videos alongside photos in galleries with streaming support | Low | ✅ Implemented |
-| **Multiple Administrators** | Support for multiple admin accounts with role-based permissions and activity tracking | Low | 📋 Planned |
+| **Multiple Administrators** | Support for multiple admin accounts with role-based permissions and activity tracking | Low | ✅ Implemented |
 | **Filtering & Export Options** | Filter photos by likes, ratings, comments, or favorites. Search by filename. Sort by date, name, size, or rating. Export filtered selections as ZIP or generate Capture One/Lightroom-compatible file lists for professional workflows | Medium | ✅ Implemented |
 
 **Status Legend:** ✅ Implemented | 🚧 In Progress | 🔄 Open | 📋 Planned