feat: basic shape.

demo/Ursa.Demo/Pages/AvatarDemo.axaml

@@ -3,7 +3,14 @@
              xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
              xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
              xmlns:u="https://irihi.tech/ursa"
+             xmlns:vm="clr-namespace:Ursa.Demo.ViewModels"
              mc:Ignorable="d" d:DesignWidth="800" d:DesignHeight="450"
              x:Class="Ursa.Demo.Pages.AvatarDemo">
-    <u:Avatar />
+    <Design.DataContext>
+        <vm:AvatarDemoViewModel />
+    </Design.DataContext>
+    <StackPanel>
+        <u:Avatar Content="{Binding Content}"
+                  Command="{Binding ClickCommand}"/>
+    </StackPanel>
 </UserControl>

demo/Ursa.Demo/ViewModels/AvatarDemoViewModel.cs

@@ -1,6 +1,16 @@
-namespace Ursa.Demo.ViewModels;
+using CommunityToolkit.Mvvm.ComponentModel;
+using CommunityToolkit.Mvvm.Input;
 
-public class AvatarDemoViewModel: ViewModelBase
+namespace Ursa.Demo.ViewModels;
+
+public partial class AvatarDemoViewModel : ViewModelBase
 {
-    
+    [ObservableProperty] private string _content = "AS";
+    [ObservableProperty] private bool _canClick = true;
+
+    [RelayCommand(CanExecute = nameof(CanClick))]
+    private void Click()
+    {
+        Content = "BM";
+    }
 }