feat: add resend creation email button and fix Handlebars template processing

- Fixed email template processing to properly handle Handlebars conditionals
  - Installed handlebars package
  - Updated processTemplate to use Handlebars.compile()
  - Now {{#if welcome_message}} blocks work correctly

- Added "Resend Creation Email" button to event details page
  - New endpoint: POST /api/admin/events/:id/resend-email
  - Button appears below "Reset Gallery Password"
  - Shows mail icon and includes success/error notifications
  - For security, resent emails show "(Aus Sicherheitsgründen nicht angezeigt)"
    instead of the actual password

- Added translations:
  - EN: "Resend Creation Email", success/error messages
  - DE: "Erstellungs-E-Mail erneut senden", success/error messages

This fixes the issue where Handlebars syntax was showing in emails and provides
a convenient way to resend the initial gallery creation email to hosts.

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

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

backend/src/routes/adminEvents.js

@@ -564,6 +564,57 @@ router.post('/:id/reset-password', adminAuth, async (req, res) => {
   }
 });
 
+// Resend creation email
+router.post('/:id/resend-email', adminAuth, async (req, res) => {
+  try {
+    const { id } = req.params;
+    
+    // Get event details
+    const event = await db('events')
+      .where('id', id)
+      .first();
+    
+    if (!event) {
+      return res.status(404).json({ error: 'Event not found' });
+    }
+    
+    // Format dates properly for the email
+    const eventDate = new Date(event.event_date);
+    const expiryDate = new Date(event.expires_at);
+    
+    // Queue the email
+    const { queueEmail } = require('../services/emailProcessor');
+    await queueEmail(id, event.host_email, 'gallery_created', {
+      host_name: event.host_name || event.host_email.split('@')[0],
+      event_name: event.event_name,
+      event_date: eventDate.toLocaleDateString('de-DE'), // Using German date format
+      gallery_link: event.share_link,
+      gallery_password: '(Aus Sicherheitsgründen nicht angezeigt)', // Security: don't show password in resent emails
+      expiry_date: expiryDate.toLocaleDateString('de-DE'),
+      welcome_message: event.welcome_message || '',
+      eventId: id
+    });
+    
+    // Log the activity
+    await db('activity_logs').insert({
+      event_id: id,
+      ip_address: req.ip,
+      user_agent: req.get('user-agent'),
+      action_type: 'email_resent',
+      action_details: JSON.stringify({ email_type: 'gallery_created' }),
+      timestamp: new Date()
+    });
+    
+    res.json({ 
+      success: true,
+      message: 'Creation email has been queued for sending'
+    });
+  } catch (error) {
+    console.error('Error resending creation email:', error);
+    res.status(500).json({ error: 'Failed to resend creation email' });
+  }
+});
+
 // Archive event
 router.post('/:id/archive', adminAuth, async (req, res) => {
   try {