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/src/middleware/maintenance.js

@@ -0,0 +1,73 @@
+const { db } = require('../database/db');
+
+// Cache maintenance mode status to avoid DB queries on every request
+let maintenanceMode = false;
+let lastCheck = 0;
+const CACHE_DURATION = 60000; // 1 minute
+
+async function checkMaintenanceMode() {
+  const now = Date.now();
+  
+  // Use cached value if recent
+  if (now - lastCheck < CACHE_DURATION) {
+    return maintenanceMode;
+  }
+  
+  try {
+    const setting = await db('app_settings')
+      .where('setting_key', 'general_maintenance_mode')
+      .where('setting_type', 'general')
+      .first();
+    
+    maintenanceMode = setting ? (setting.setting_value === 'true' || setting.setting_value === true) : false;
+    lastCheck = now;
+    
+    return maintenanceMode;
+  } catch (error) {
+    console.error('Error checking maintenance mode:', error);
+    return false;
+  }
+}
+
+// Middleware to enforce maintenance mode
+async function maintenanceMiddleware(req, res, next) {
+  // Skip maintenance check for certain paths
+  const skipPaths = [
+    '/api/admin/login',
+    '/api/admin/auth/login',
+    '/api/public/settings',
+    '/health'
+  ];
+  
+  // Allow static assets (uploads, favicons, logos)
+  const isStaticAsset = req.path.startsWith('/uploads/') || 
+                       req.path.startsWith('/favicons/') || 
+                       req.path.startsWith('/logos/');
+  
+  // Allow admin routes if admin is authenticated
+  const isAdminRoute = req.path.startsWith('/api/admin');
+  const hasAdminAuth = req.headers.authorization?.startsWith('Bearer ');
+  
+  if (skipPaths.includes(req.path) || isStaticAsset || (isAdminRoute && hasAdminAuth)) {
+    return next();
+  }
+  
+  const inMaintenance = await checkMaintenanceMode();
+  
+  if (inMaintenance && !isAdminRoute) {
+    return res.status(503).json({
+      error: 'Service Unavailable',
+      message: 'The system is currently undergoing maintenance. Please try again later.',
+      maintenance: true
+    });
+  }
+  
+  next();
+}
+
+// Function to clear cache when settings change
+function clearMaintenanceCache() {
+  lastCheck = 0;
+}
+
+module.exports = { maintenanceMiddleware, clearMaintenanceCache };