Fix heartbeat false positive right after startup (#400)

Ink Canvas/App.xaml.cs

@@ -1079,6 +1079,8 @@ namespace Ink_Canvas
             {
                 isStartupComplete = true;
                 startupCompleteHeartbeat = DateTime.Now;
+                // 启动完成时重置心跳时间，避免启动阶段主线程长时间忙碌导致误判为“无响应”
+                lastHeartbeat = startupCompleteHeartbeat;
                 if (_isSplashScreenShown && splashScreenStartTime != DateTime.MinValue)
                 {
                     LogHelper.WriteLogToFile($"启动完成心跳已记录，启动画面显示时长: {(startupCompleteHeartbeat - splashScreenStartTime).TotalSeconds:F2}秒");