feat: add demo.

demo/Ursa.Demo/Pages/PopConfirmDemo.axaml.cs

@@ -0,0 +1,25 @@
+using Avalonia;
+using Avalonia.Controls;
+using Avalonia.Markup.Xaml;
+using Ursa.Controls;
+using Ursa.Demo.ViewModels;
+
+namespace Ursa.Demo.Pages;
+
+public partial class PopConfirmDemo : UserControl
+{
+    public PopConfirmDemo()
+    {
+        InitializeComponent();
+    }
+
+    protected override void OnAttachedToVisualTree(VisualTreeAttachmentEventArgs e)
+    {
+        base.OnAttachedToVisualTree(e);
+        if (this.DataContext is not PopConfirmDemoViewModel vm) return;
+        var manager = WindowToastManager.TryGetToastManager(TopLevel.GetTopLevel(this), out var m)
+            ? m
+            : new WindowToastManager(TopLevel.GetTopLevel(this));
+        vm.ToastManager = manager;
+    }
+}