feat: initialize, setup demo. make sure MVVM works.

demo/Ursa.Demo/ViewModels/MainViewViewModel.cs

@@ -53,6 +53,7 @@ public class MainViewViewModel : ViewModelBase
             MenuKeys.MenuKeyTimeline => new TimelineDemoViewModel(),
             MenuKeys.MenuKeyTwoTonePathIcon => new TwoTonePathIconDemoViewModel(),
             MenuKeys.MenuKeyThemeToggler => new ThemeTogglerDemoViewModel(),
+            MenuKeys.MenuKeyToolBar => new ToolBarDemoViewModel(),
         };
     }
 }