refactor：拆分 API 路由与请求校验，统一 final 类和代码风格

app/Events/DrawCountdownBroadcast.php

@@ -3,13 +3,13 @@
 namespace App\Events;
 
 use Illuminate\Broadcasting\Channel;
+use Illuminate\Queue\SerializesModels;
+use Illuminate\Foundation\Events\Dispatchable;
 use Illuminate\Broadcasting\InteractsWithSockets;
 use Illuminate\Contracts\Broadcasting\ShouldBroadcastNow;
-use Illuminate\Foundation\Events\Dispatchable;
-use Illuminate\Queue\SerializesModels;
 
 /** 界面文档 §2.1：`draw.countdown` */
-class DrawCountdownBroadcast implements ShouldBroadcastNow
+final class DrawCountdownBroadcast implements ShouldBroadcastNow
 {
     use Dispatchable, InteractsWithSockets, SerializesModels;