refactor(activity): 优化启动页跳转延迟及子设备页面稳定性，修复导航栏闪烁问题

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

app/src/main/java/com/shuwei/dish/match/scale/ScaleServiceManager.kt

@@ -54,6 +54,10 @@ object ScaleServiceManager {
         get() = wsServer?.onConnectionChanged
         set(value) { wsServer?.onConnectionChanged = value }
 
+    /** 当前是否有主设备连接（仅子设备使用） */
+    val isMasterConnected: Boolean
+        get() = wsServer?.isConnected == true
+
     /**
      * 启动所有秤服务，在 Application.onCreate() 中调用
      */

app/src/main/java/com/shuwei/dish/match/scale/ScaleWebSocketServer.kt

@@ -28,6 +28,10 @@ class ScaleWebSocketServer(private val deviceId: String, private val context: Co
     /** 主设备连接状态变化回调：true=已连接，false=已断开；在主线程外调用，需自行切换线程 */
     var onConnectionChanged: ((connected: Boolean) -> Unit)? = null
 
+    /** 当前是否有主设备连接 */
+    val isConnected: Boolean
+        get() = server?.connections?.isNotEmpty() == true
+
     /** 每个秤地址的最近一次推送时间，用于节流 */
     private val lastPushTime = mutableMapOf<Int, Long>()