fix: 去抖合并后更新横幅数字

问题：多条消息同时到达，第一条横幅显示1，后续被去抖暂存。
1s后合并处理emit NewTaskArrived(count=3)，但MainActivity
只监听MqttMessageReceived更新横幅，不监听NewTaskArrived。

修复：MainActivity同时监听NewTaskArrived，去抖合并后更新横幅。

时序：消息1→横幅"1条" → 消息2,3暂存 → 1s后合并→横幅更新"3条"

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

app/src/main/java/com/xiaoqu/watch/app/MainActivity.kt

@@ -80,12 +80,23 @@ class MainActivity : AppCompatActivity() {
     private fun observeMqttMessages() {
         activityScope.launch {
             eventBus.events.collect { event ->
-                if (event is AppEvent.MqttMessageReceived && event.type == 1) {
-                    notificationManager.onNewTaskMessage(event.rawJson)
-                    val count = notificationManager.pendingCount
-                    if (count > 0) {
-                        notificationBanner.show(count)
+                when (event) {
+                    is AppEvent.MqttMessageReceived -> {
+                        if (event.type == 1) {
+                            notificationManager.onNewTaskMessage(event.rawJson)
+                            val count = notificationManager.pendingCount
+                            if (count > 0) {
+                                notificationBanner.show(count)
+                            }
+                        }
                     }
+                    // 去抖合并完成后 → 更新横幅数字
+                    is AppEvent.NewTaskArrived -> {
+                        if (event.count > 0) {
+                            notificationBanner.show(event.count)
+                        }
+                    }
+                    else -> {}
                 }
             }
         }