feat(ui): animate folder expand in the sidebar

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

@@ -18,6 +18,8 @@ public sealed partial class ListFolderNavItemViewModel : ViewModelBase
     [ObservableProperty] private string _iconKey = "Folder";
     /// <summary>Hex colour for name + guide line; null = theme default.</summary>
     [ObservableProperty] private string? _color;
+    /// <summary>Set on the first user toggle so the expand animation skips folders that load already open.</summary>
+    [ObservableProperty] private bool _animateExpand;
     [ObservableProperty]
     [NotifyPropertyChangedFor(nameof(ShowCount))]
     private bool _isCollapsed;

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

@@ -730,6 +730,7 @@ public sealed partial class ListsIslandViewModel : ViewModelBase, IDisposable
     private void ToggleFolder(ListFolderNavItemViewModel? folder)
     {
         if (folder is null) return;
+        folder.AnimateExpand = true;
         folder.IsCollapsed = !folder.IsCollapsed;
         if (_folderCollapseCts.TryGetValue(folder.Id, out var previous)) previous.Cancel();
         var cts = new CancellationTokenSource();