修复：全员清屏广播不生效

- ScreenCleared 改用 ShouldBroadcastNow 绕过队列，避免 Horizon 未重启问题
- Echo 监听移入 DOMContentLoaded + 500ms 重试，确保 window.Echo 就绪后再注册
- 添加 console.log 便于调试

app/Events/ScreenCleared.php

@@ -14,11 +14,11 @@ namespace App\Events;
 
 use Illuminate\Broadcasting\InteractsWithSockets;
 use Illuminate\Broadcasting\PresenceChannel;
-use Illuminate\Contracts\Broadcasting\ShouldBroadcast;
+use Illuminate\Contracts\Broadcasting\ShouldBroadcastNow;
 use Illuminate\Foundation\Events\Dispatchable;
 use Illuminate\Queue\SerializesModels;
 
-class ScreenCleared implements ShouldBroadcast
+class ScreenCleared implements ShouldBroadcastNow
 {
     use Dispatchable, InteractsWithSockets, SerializesModels;