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 <[email protected]>

backend/src/routes/events.js

@@ -79,16 +79,14 @@ router.post('/', adminAuth, [
     });
     
     // Queue creation email
-    await db('email_queue').insert({
-      event_id: eventId,
-      recipient_email: host_email,
-      email_type: 'creation',
-      email_data: JSON.stringify({
-        event_name,
-        share_link: shareLink,
-        password,
-        expires_at
-      })
+    const { queueEmail } = require('../services/emailProcessor');
+    await queueEmail(eventId, host_email, 'gallery_created', {
+      host_name: host_email.split('@')[0], // Extract name from email
+      event_name,
+      event_date: new Date(event_date).toLocaleDateString(),
+      gallery_link: shareLink,
+      gallery_password: password,
+      expiry_date: expires_at.toLocaleDateString()
     });
     
     res.json({