fix: 解绑时重置bindHandled标记 + 绑定加Toast调试

解绑后bindHandled没重置导致再次绑定时消息被跳过。

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

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

@@ -140,6 +140,7 @@ class MainActivity : AppCompatActivity() {
                                 android.widget.Toast.makeText(this@MainActivity, "收到解绑消息", android.widget.Toast.LENGTH_SHORT).show()
                                 bluetoothScanManager.stop()
                                 userPrefs.clear()
+                                bindHandled = false  // 重置绑定标记，允许重新绑定
                                 try {
                                     val navHost = supportFragmentManager
                                         .findFragmentById(R.id.nav_host_fragment) as? NavHostFragment
@@ -257,7 +258,11 @@ class MainActivity : AppCompatActivity() {
 
     /** 处理 MQTT type=2 绑定消息（Activity 级别，不受 Fragment 生命周期影响） */
     private fun handleBindMessage(rawJson: String) {
-        if (bindHandled) return
+        android.widget.Toast.makeText(this, "收到绑定消息", android.widget.Toast.LENGTH_SHORT).show()
+        if (bindHandled) {
+            android.widget.Toast.makeText(this, "绑定已处理过，跳过", android.widget.Toast.LENGTH_SHORT).show()
+            return
+        }
         bindHandled = true
 
         try {