feat(notifications): add alerts queries validator

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/Appwrite/Utopia/Database/Validator/Queries/Alerts.php

@@ -0,0 +1,23 @@
+<?php
+
+namespace Appwrite\Utopia\Database\Validator\Queries;
+
+class Alerts extends Base
+{
+    public const ALLOWED_ATTRIBUTES = [
+        'read',
+        'type',
+        'channel',
+        'messageId',
+        'projectId',
+    ];
+
+    /**
+     * Expression constructor
+     *
+     */
+    public function __construct()
+    {
+        parent::__construct('alerts', self::ALLOWED_ATTRIBUTES);
+    }
+}