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 <noreply@anthropic.com>

frontend/src/contexts/index.ts

@@ -1,4 +1,5 @@
 export { GalleryAuthProvider, useGalleryAuth } from './GalleryAuthContext';
 export { AdminAuthProvider, useAdminAuth } from './AdminAuthContext';
 export { ThemeProvider, useTheme, PRESET_THEMES } from './ThemeContext';
-export type { ThemeConfig, EventTheme } from './ThemeContext';
+export type { ThemeConfig, EventTheme } from './ThemeContext';
+export { MaintenanceProvider, useMaintenanceMode } from './MaintenanceContext';