feat: use numpad button.

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

@@ -0,0 +1,14 @@
+using Avalonia;
+using Avalonia.Controls;
+using Avalonia.Input;
+using Avalonia.Markup.Xaml;
+
+namespace Ursa.Demo.Pages;
+
+public partial class NumPadDemo : UserControl
+{
+    public NumPadDemo()
+    {
+        InitializeComponent();
+    }
+}