refactor(config): consolidate commit types into CommitTypeRegistry

Replaces six scattered "chore" literals across TaskEntity, ListEntity,
WorkerHub, ListsIslandViewModel, ListNavItemViewModel and the inline
commit type list in ListSettingsModalViewModel.

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

@@ -163,7 +163,7 @@ public sealed partial class ListsIslandViewModel : ViewModelBase
         {
             Id = Guid.NewGuid().ToString("N"),
             Name = "New list",
-            DefaultCommitType = "chore",
+            DefaultCommitType = CommitTypeRegistry.DefaultType,
             CreatedAt = DateTime.UtcNow,
         };