feat: 彻底禁用 Flarum 邮件通知

- 从驱动层移除 EmailNotificationDriver，禁止所有邮件通知发送
- 新用户注册时自动关闭邮件通知偏好兜底
- 站点通知保持不变

extend.php

@@ -0,0 +1,15 @@
+<?php
+
+namespace MetaZone\DisableEmailNotifications;
+
+use Flarum\Extend;
+use Flarum\User\Event\Registered;
+use MetaZone\DisableEmailNotifications\Listener\DisableEmailNotificationsListener;
+
+return [
+    (new Extend\Event)
+        ->listen(Registered::class, DisableEmailNotificationsListener::class),
+
+    // 从驱动层彻底移除邮件通知，不依赖偏好设置
+    new RemoveEmailDriver(),
+];