Fix brand theme application and add comprehensive translations

- Fixed theme not being reflected on gallery and admin login pages
- Created GlobalThemeProvider to apply themes globally
- Updated gallery and admin login pages to use dynamic CSS variables
- Added complete translations for all admin sections in English and German:
  - Notifications management
  - Event view and creation
  - Photo upload functionality
  - Category management
  - Archive page view
  - Analytics dashboard
  - Branding and theme settings
  - System settings
  - CMS page management
  - Email configuration
- Fixed admin photo management display issues
- Fixed photo upload category assignment
- Added password reset functionality for galleries
- Improved error handling and user feedback

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <[email protected]>

frontend/src/components/gallery/GalleryView.tsx

@@ -231,14 +231,6 @@ export const GalleryView: React.FC<GalleryViewProps> = ({ slug, event }) => {
         <ExpirationBanner daysRemaining={daysUntilExpiration} expiresAt={event.expires_at} />
       )}
 
-      {/* Welcome Message */}
-      {event.welcome_message && (
-        <div className="mt-6">
-          <div className="bg-primary-50 border border-primary-200 rounded-lg p-4">
-            <p className="text-primary-900">{event.welcome_message}</p>
-          </div>
-        </div>
-      )}
 
       {/* Search and Filters */}
       <div className="mt-6">