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>

backend/scripts/test-admin-photo.js

@@ -0,0 +1,55 @@
+const axios = require('axios');
+
+async function testAdminPhotoEndpoint() {
+  try {
+    // First login
+    console.log('1. Logging in as admin...');
+    const loginResponse = await axios.post('http://localhost:3000/api/admin/auth/login', {
+      username: 'admin',
+      password: 'admin123'
+    });
+    
+    const token = loginResponse.data.token;
+    console.log('✓ Login successful, got token');
+    
+    // Test thumbnail endpoint
+    console.log('\n2. Testing thumbnail endpoint for photo 1688...');
+    try {
+      const thumbResponse = await axios.get('http://localhost:3000/api/admin/events/12/thumbnail/1688', {
+        headers: {
+          Authorization: `Bearer ${token}`
+        },
+        responseType: 'arraybuffer'
+      });
+      
+      console.log('✓ Thumbnail request successful');
+      console.log('  Response headers:', thumbResponse.headers);
+      console.log('  Data size:', thumbResponse.data.length, 'bytes');
+    } catch (error) {
+      console.error('✗ Thumbnail request failed:', error.response?.status, error.response?.data?.toString());
+    }
+    
+    // Test from frontend proxy port
+    console.log('\n3. Testing through nginx proxy (port 3001)...');
+    try {
+      const proxyResponse = await axios.get('http://localhost:3001/api/admin/events/12/thumbnail/1688', {
+        headers: {
+          Authorization: `Bearer ${token}`,
+          Origin: 'http://localhost:3005'
+        },
+        responseType: 'arraybuffer'
+      });
+      
+      console.log('✓ Proxy request successful');
+      console.log('  Response headers:', proxyResponse.headers);
+      console.log('  Data size:', proxyResponse.data.length, 'bytes');
+    } catch (error) {
+      console.error('✗ Proxy request failed:', error.response?.status, error.response?.data?.toString());
+    }
+    
+  } catch (error) {
+    console.error('Error:', error.message);
+  }
+}
+
+testAdminPhotoEndpoint();