Fix FCM token registration and add queue reminder alerts

- Fix silent insert failure in FCM token registration (missing NOT NULL
  refresh_token column) so WebView app tokens are actually stored
- Add 1-minute queue reminder cron that re-sends FCM alerts for calls
  still waiting, with transient-based throttle to prevent duplicates
- Send FCM cancel on queue dequeue (answered/hangup/timeout), not just
  on final call status webhook
- Clean up new cron hook on plugin deactivation

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

includes/class-twp-webhooks.php

@@ -1276,10 +1276,24 @@ class TWP_Webhooks {
         
         if ($updated) {
             error_log('TWP Queue Action: Updated call status to ' . $status);
+
+            // Cancel FCM queue alerts when call leaves the queue for any reason
+            if (in_array($status, array('answered', 'hangup', 'transferred', 'timeout', 'completed'))) {
+                $queued_call = $wpdb->get_row($wpdb->prepare(
+                    "SELECT queue_id FROM $table_name WHERE call_sid = %s",
+                    $call_sid
+                ));
+                if ($queued_call) {
+                    require_once plugin_dir_path(__FILE__) . 'class-twp-fcm.php';
+                    $fcm = new TWP_FCM();
+                    $fcm->cancel_queue_alert_for_queue($queued_call->queue_id, $call_sid);
+                    error_log('TWP Queue Action: Sent FCM cancel for call ' . $call_sid);
+                }
+            }
         } else {
             error_log('TWP Queue Action: No call found to update with SID ' . $call_sid);
         }
-        
+
         // Return empty response - this is just for tracking
         return $this->send_twiml_response('<Response></Response>');
     }