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/pages/admin/SettingsPage.tsx

@@ -18,7 +18,7 @@ import { useTranslation } from 'react-i18next';
 export const SettingsPage: React.FC = () => {
   const [activeTab, setActiveTab] = useState<'general' | 'storage' | 'security' | 'categories'>('general');
   const queryClient = useQueryClient();
-  const { t } = useTranslation();
+  const { t, i18n } = useTranslation();
 
   // Fetch settings
   const { data: settings, isLoading } = useQuery({
@@ -60,6 +60,11 @@ export const SettingsPage: React.FC = () => {
 
   React.useEffect(() => {
     if (settings) {
+      // Set the language if it's different from current
+      if (settings.general_default_language && settings.general_default_language !== i18n.language) {
+        i18n.changeLanguage(settings.general_default_language);
+      }
+      
       // Extract general settings
       setGeneralSettings({
         site_url: settings.general_site_url || '',