feat(ui): session skills registry tab + per-level selectors

src/ClaudeDo.Ui/ViewModels/Agent/SelectableSkillViewModel.cs

@@ -0,0 +1,23 @@
+using CommunityToolkit.Mvvm.ComponentModel;
+
+namespace ClaudeDo.Ui.ViewModels.Agent;
+
+/// <summary>
+/// One installed session skill shown as a checkbox row. Reused by the global (General tab),
+/// list, and task selectors — selection is additive-union across all three levels, so this
+/// is deliberately just a name + checked flag with no inheritance/override state.
+/// </summary>
+public sealed partial class SelectableSkillViewModel : ViewModelBase
+{
+    public string Name { get; }
+    public string Description { get; }
+
+    [ObservableProperty] private bool _isSelected;
+
+    public SelectableSkillViewModel(string name, string description = "", bool isSelected = false)
+    {
+        Name = name;
+        Description = description;
+        _isSelected = isSelected;
+    }
+}