Add SplashScreen view import and update initialization

Importing the SplashScreen view allows the application to display a splash screen during launch. Additionally, updating the OnFrameworkInitializationCompleted method to be asynchronous supports potential future asynchronous operations.

src/Gml.Launcher/App.axaml.cs

@@ -3,6 +3,7 @@
 using Avalonia.Markup.Xaml;
 using Gml.Launcher.ViewModels;
 using Gml.Launcher.Views;
+using Gml.Launcher.Views.SplashScreen;
 
 namespace Gml.Launcher;
 
@@ -13,7 +14,7 @@ public override void Initialize()
         AvaloniaXamlLoader.Load(this);
     }
 
-    public override void OnFrameworkInitializationCompleted()
+    public override async void OnFrameworkInitializationCompleted()
     {
         if (ApplicationLifetime is IClassicDesktopStyleApplicationLifetime desktop)
         {