Implement multi-language email templates

- Add language columns to email_templates table (subject_en/de, body_html_en/de, body_text_en/de)
- Update adminEmail.js routes to support language-specific templates
- Create EmailProcessor service to handle language selection based on recipient
- Update EmailConfigPage component with language tabs similar to CMS pages
- Add German translations for all email templates
- Update all email queue usage to use proper template keys
- Add missing email templates (gallery_expired, archive_complete)
- Integrate email processor service into main server startup

The system now automatically selects the appropriate language (English/German) based on the recipient's email domain or preferences.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

backend/server.js

@@ -8,6 +8,7 @@ const path = require('path');
 const { initializeDatabase } = require('./src/database/db');
 const { startFileWatcher } = require('./src/services/fileWatcher');
 const { startExpirationChecker } = require('./src/services/expirationChecker');
+const { startEmailQueueProcessor } = require('./src/services/emailProcessor');
 const { maintenanceMiddleware } = require('./src/middleware/maintenance');
 const { sessionTimeoutMiddleware } = require('./src/middleware/sessionTimeout');
 const logger = require('./src/utils/logger');
@@ -141,6 +142,9 @@ async function startServer() {
     // Start expiration checker
     startExpirationChecker();
     
+    // Start email queue processor
+    startEmailQueueProcessor();
+    
     app.listen(PORT, () => {
       logger.info(`Server running on port ${PORT}`);
       logger.info(`Admin interface: ${process.env.ADMIN_URL || 'http://localhost:3000'}`);