refactor(migration): 统一数据库迁移基类为 AbstractMigration

- 将所有迁移类继承自 Phinx\Migration\AbstractMigration
- 替换旧的 think\migration\Migrator 基类
- 更新相关的 use 语句引入 Phinx 类库
- 保持原有的迁移逻辑和方法签名不变
- 确保严格类型声明在文件顶部正确设置

database/migrations/20250917093821_notifications_timstamp.php

@@ -1,9 +1,9 @@
 <?php
 
-use think\migration\Migrator;
+use Phinx\Migration\AbstractMigration;
 use think\migration\db\Column;
 
-class NotificationsTimstamp extends Migrator
+class NotificationsTimstamp extends AbstractMigration
 {
     /**
      * Change Method.