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/package.json

@@ -1,7 +1,7 @@
 {
   "name": "picpeak-frontend",
   "private": true,
-  "version": "1.1.15",
+  "version": "2.2.1",
   "type": "module",
   "scripts": {
     "dev": "vite",