优化：禁言提示显示操作者 + 被禁言发言改用持久提示

- UserMuted 事件增加 operator 字段，禁言通知显示管理员名字
- 输入框 placeholder 显示操作者名字
- 被禁言用户发言时改为在包厢窗口显示红色持久提示（替代 alert 弹窗）

app/Events/UserMuted.php

@@ -32,6 +32,7 @@ class UserMuted implements ShouldBroadcast
         public readonly string $username,
         public readonly int $muteTime,
         public readonly string $message = '',
+        public readonly string $operator = '',
     ) {}
 
     /**
@@ -54,12 +55,13 @@ class UserMuted implements ShouldBroadcast
     public function broadcastWith(): array
     {
         $statusMessage = $this->message ?: ($this->muteTime > 0
-            ? "用户 [{$this->username}] 已被禁言 {$this->muteTime} 分钟。"
+            ? "管理员 [{$this->operator}] 已将 [{$this->username}] 禁言 {$this->muteTime} 分钟。"
             : "用户 [{$this->username}] 已被解除禁言。");
 
         return [
             'username' => $this->username,
             'mute_time' => $this->muteTime,
+            'operator' => $this->operator,
             'message' => $statusMessage,
         ];
     }