fix: Use OpenPlayground() method to load Playground sample correctly

Co-authored-by: MartinZikmund <1075116+MartinZikmund@users.noreply.github.com>

Author: Copilot

src/SamplesApp/SamplesApp.Shared/App.xaml.cs

@@ -418,7 +418,7 @@ private async void HandleLaunchArguments(LaunchActivatedEventArgs launchActivate
 
 			if (SampleControl.Presentation.SampleChooserViewModel.Instance is { } vm && vm.CurrentSelectedSample is null)
 			{
-				vm.SetSelectedSample(CancellationToken.None, "Playground", "Playground");
+				vm.OpenPlayground();
 			}
 		}