fix: remove updated_at field from password reset query

- The events table doesn't have an updated_at column
- Fixes PostgreSQL error 42703 when resetting passwords
- Password hash update now works correctly

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

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

backend/src/routes/adminEvents.js

@@ -534,8 +534,7 @@ router.post('/:id/reset-password', adminAuth, async (req, res) => {
     await db('events')
       .where('id', id)
       .update({
-        password_hash: passwordHash,
-        updated_at: new Date()
+        password_hash: passwordHash
       });
 
     // Log activity