fix: remove dual retry path in check_pending_site_created (#797)

When a stale is_publishing flag is detected and reset, the code was
both enqueuing wu_async_publish_pending_site via Action Scheduler AND
returning publish_status=stopped to the frontend. This created two
competing retry sources that could trigger double site creation.

Remove the wu_enqueue_async_action call. The frontend polling loop
retries on 'stopped' status, and the existing AS scheduled action
will pick up the reset flag on its next run — a single retry path
is sufficient.

Fixes #793

Author: superdav42

inc/managers/class-membership-manager.php

@@ -219,11 +219,13 @@ public function check_pending_site_created() {
 			);
 
 			/*
-			 * Re-enqueue the async action so Action Scheduler retries
-			 * the site creation without waiting for the next cron tick.
+			 * Return 'stopped' so the frontend polling loop retries.
+			 * Do NOT also enqueue wu_async_publish_pending_site here —
+			 * that would create two competing retry sources (Action
+			 * Scheduler + frontend) and risk double site creation.
+			 * The existing AS scheduled action will pick up the reset
+			 * flag on its next run.
 			 */
-			wu_enqueue_async_action('wu_async_publish_pending_site', ['membership_id' => $membership->get_id()], 'membership');
-
 			wp_send_json(['publish_status' => 'stopped']);
 
 			exit;