feat(ui): scaffold islands shell and child VMs

src/ClaudeDo.Ui/ViewModels/Islands/ListNavItemViewModel.cs

@@ -0,0 +1,12 @@
+using CommunityToolkit.Mvvm.ComponentModel;
+
+namespace ClaudeDo.Ui.ViewModels.Islands;
+
+public sealed partial class ListNavItemViewModel : ViewModelBase
+{
+    public required string Id { get; init; }
+    public required string Name { get; init; }
+    [ObservableProperty] private int _count;
+    [ObservableProperty] private bool _isActive;
+    public string? IconKey { get; init; }
+}