Fix parse error in notifications.php: escape inner quotes in LIKE string

The $statusSql double-quoted string contained '%"status":%' which caused
PHP to terminate the string at the inner double quotes, resulting in a
parse error (unexpected identifier 'status') on the beta server.

Also cleared stale stats cache that stored by_assignee in old name=>count
map format instead of the current array-of-objects format.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

api/notifications.php

@@ -127,7 +127,7 @@ $statusSql = "SELECT DISTINCT
     AND al.entity_type = 'ticket'
     AND al.user_id != ?
     AND al.created_at >= DATE_SUB(NOW(), INTERVAL 7 DAY)
-    AND al.details LIKE '%"status":%'
+    AND al.details LIKE '%\"status\":%'
   ORDER BY al.created_at DESC
   LIMIT 10";