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/Repository/NotificationRepositoryInterface.php

@@ -0,0 +1,26 @@
+<?php
+
+namespace MintyPHP\Module\Notifications\Repository;
+
+interface NotificationRepositoryInterface
+{
+    /** @return int|false Insert ID on success, false on failure */
+    public function create(array $data): int|false;
+
+    /**
+     * @return list<array<string, mixed>>
+     */
+    public function listByUser(int $userId, int $limit, int $offset): array;
+
+    public function countUnreadByUser(int $userId): int;
+
+    public function markRead(int $id, int $userId): bool;
+
+    public function markAllReadByUser(int $userId): int;
+
+    public function delete(int $id, int $userId): bool;
+
+    public function deleteAllByUser(int $userId): int;
+
+    public function purgeReadOlderThanDays(int $days): int;
+}