fix: 添加缺失的R import，修复编译错误

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

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

@@ -7,6 +7,7 @@ import android.view.View
 import androidx.navigation.findNavController
 import androidx.activity.OnBackPressedCallback
 import androidx.appcompat.app.AppCompatActivity
+import com.xiaoqu.watch.R
 import com.xiaoqu.watch.databinding.ActivityMainBinding
 import com.xiaoqu.watch.event.AppEvent
 import com.xiaoqu.watch.event.EventBus