Fix admin queue waiting calls filter error

- Change ajax_get_waiting_calls response format to return array directly
- Fixes JavaScript error "waitingCalls.filter is not a function"
- Ensures compatibility with frontend filter operations

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

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

admin/class-twp-admin.php

@@ -3973,10 +3973,7 @@ class TWP_Admin {
             ORDER BY c.position ASC
         ", $user_id));
         
-        wp_send_json_success(array(
-            'count' => count($waiting_calls),
-            'calls' => $waiting_calls
-        ));
+        wp_send_json_success($waiting_calls);
     }
     
     /**