Fix event creation errors

- Fix req.user undefined error by using req.admin from middleware
- Return proper ISO date strings in event creation response
- Include created_at in response for frontend navigation

This fixes the 500 error when creating events and ensures the frontend
receives the expected data format for navigation.

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

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

backend/src/routes/adminEvents.js

@@ -85,7 +85,7 @@ router.post('/', adminAuth, [
     await logActivity('event_created', 
       { event_type, expires_at }, 
       eventId, 
-      { type: 'admin', id: req.user.id, name: req.user.username }
+      { type: 'admin', id: req.admin.id, name: req.admin.username }
     );
     
     // Queue creation email
@@ -108,7 +108,8 @@ router.post('/', adminAuth, [
       event_name,
       event_type,
       share_link: shareLink,
-      expires_at
+      expires_at: expires_at.toISOString(),
+      created_at: new Date().toISOString()
     });
   } catch (error) {
     console.error('Error creating event:', error);