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/Providers/NotificationsSessionProvider.php

@@ -0,0 +1,35 @@
+<?php
+
+namespace MintyPHP\Module\Notifications\Providers;
+
+use MintyPHP\App\AppContainer;
+use MintyPHP\App\Module\Contracts\SessionProvider;
+use MintyPHP\Http\SessionStoreInterface;
+use MintyPHP\Module\Notifications\Service\NotificationService;
+
+final class NotificationsSessionProvider implements SessionProvider
+{
+    private const SESSION_KEY = 'module.notifications.unread_count';
+
+    public function populate(array $user, AppContainer $container): void
+    {
+        $userId = (int) ($user['id'] ?? 0);
+        if ($userId <= 0) {
+            unset($_SESSION[self::SESSION_KEY]);
+            return;
+        }
+
+        $sessionStore = $container->get(SessionStoreInterface::class);
+        $service = $container->get(NotificationService::class);
+        if (!$sessionStore instanceof SessionStoreInterface || !$service instanceof NotificationService) {
+            return;
+        }
+
+        $sessionStore->set(self::SESSION_KEY, $service->unreadCount($userId));
+    }
+
+    public function clear(): void
+    {
+        unset($_SESSION[self::SESSION_KEY]);
+    }
+}