Add foundation

Toolkit.Foundation/CommandViewModel.cs

@@ -0,0 +1,17 @@
+using CommunityToolkit.Mvvm.Input;
+
+namespace Toolkit.Foundation;
+
+public partial class CommandViewModel(IServiceProvider serviceProvider,
+    IServiceFactory serviceFactory,
+    IPublisher publisher,
+    ISubscriber subscriber,
+    IDisposer disposer) :
+    ObservableViewModel(serviceProvider, serviceFactory, publisher, subscriber, disposer)
+{
+    public IRelayCommand InvokeCommand => 
+        new AsyncRelayCommand(InvokeAsync);
+
+    protected virtual Task InvokeAsync() => 
+        Task.CompletedTask;
+}