feat(ui): list reordering, quick actions, and resizable modals

- Drag-to-reorder user lists in the sidebar, persisted via a new
  list sort_order column (AddListSortOrder migration, backfilled by
  creation time) and ListRepository.ReorderAsync
- "Open in Explorer" / "Open in Terminal" context-menu actions on lists
- "Clear all completed" button on the Tasks island
- Inline-edit subtask titles (empty text deletes the step) and
  click-to-copy task ID in the Details island
- Make modal and planning windows resizable (BorderOnly decorations
  with min sizes) instead of fixed-size borderless

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

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

@@ -12,6 +12,8 @@ public sealed partial class ListNavItemViewModel : ViewModelBase
     [ObservableProperty] private bool _isActive;
     [ObservableProperty] private string? _workingDir;
     [ObservableProperty] private string _defaultCommitType = CommitTypeRegistry.DefaultType;
+    [ObservableProperty] private bool _dropHintAbove;
+    [ObservableProperty] private bool _dropHintBelow;
     public string? IconKey { get; init; }
     public string? DotColorKey { get; init; }
 }