feat(lists): assign a colour to a sidebar folder

Tints the folder name and its guide line; picked from a swatch row in the folder settings.

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

@@ -16,6 +16,8 @@ public sealed partial class ListFolderNavItemViewModel : ViewModelBase
     public string? ParentFolderId { get; set; }
     [ObservableProperty] private string _name = "";
     [ObservableProperty] private string _iconKey = "Folder";
+    /// <summary>Hex colour for name + guide line; null = theme default.</summary>
+    [ObservableProperty] private string? _color;
     [ObservableProperty]
     [NotifyPropertyChangedFor(nameof(ShowCount))]
     private bool _isCollapsed;

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

@@ -352,6 +352,7 @@ public sealed partial class ListsIslandViewModel : ViewModelBase, IDisposable
                     Id = f.Id,
                     Name = f.Name,
                     IconKey = f.Icon ?? ListFolderIcon,
+                    Color = f.Color,
                     IsCollapsed = f.IsCollapsed,
                     ParentFolderId = f.ParentFolderId,
                 };
@@ -758,7 +759,7 @@ public sealed partial class ListsIslandViewModel : ViewModelBase, IDisposable
         if (folder is null || Dialogs is null || _services is null) return;
         var vm = _services.GetRequiredService<ListSettingsModalViewModel>();
         vm.ErrorReported += msg => ErrorReported?.Invoke(msg);
-        vm.BeginLoadFolder(folder.Id, folder.Name, folder.IconKey);
+        vm.BeginLoadFolder(folder.Id, folder.Name, folder.IconKey, folder.Color);
         await Dialogs.ShowListSettingsAsync(vm);
         // Rename, re-icon and delete all change the folder header (and delete releases its lists
         // back to the top level) — one reload covers every outcome.