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/hooks/useSessionTimeout.ts

@@ -0,0 +1,40 @@
+import { useEffect, useCallback } from 'react';
+import { useAdminAuth } from '../contexts';
+import { api } from '../config/api';
+
+// Hook to handle session timeout
+export const useSessionTimeout = () => {
+  const { logout } = useAdminAuth();
+  
+  const handleSessionTimeout = useCallback((error: any) => {
+    if (error?.response?.data?.code === 'SESSION_TIMEOUT') {
+      // Clear local auth state
+      logout();
+      // Redirect to login with message
+      window.location.href = '/admin/login?session=expired';
+      return true;
+    }
+    return false;
+  }, [logout]);
+  
+  useEffect(() => {
+    // Add response interceptor to handle session timeout
+    const interceptor = api.interceptors.response.use(
+      response => response,
+      error => {
+        if (handleSessionTimeout(error)) {
+          // Don't propagate the error if it was a session timeout
+          return Promise.reject(new Error('Session expired'));
+        }
+        return Promise.reject(error);
+      }
+    );
+    
+    // Clean up interceptor on unmount
+    return () => {
+      api.interceptors.response.eject(interceptor);
+    };
+  }, [handleSessionTimeout]);
+  
+  return { handleSessionTimeout };
+};