feat: add notifications module with bell UI, event listeners, and cleanup job

In-app notification system with topbar bell icon, dropdown panel,
mark-as-read/dismiss actions, and scheduled cleanup of old read
notifications. Includes event listeners for user.created and
user.deleted events, authorization policy, and full test coverage.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

modules/notifications/lib/Module/Notifications/Service/NotificationRepositoryFactory.php

@@ -0,0 +1,16 @@
+<?php
+
+namespace MintyPHP\Module\Notifications\Service;
+
+use MintyPHP\Module\Notifications\Repository\NotificationRepository;
+use MintyPHP\Module\Notifications\Repository\NotificationRepositoryInterface;
+
+class NotificationRepositoryFactory
+{
+    private ?NotificationRepository $notificationRepository = null;
+
+    public function createNotificationRepository(): NotificationRepositoryInterface
+    {
+        return $this->notificationRepository ??= new NotificationRepository();
+    }
+}