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/Views/Modals/WorktreesOverviewModalView.axaml

@@ -11,7 +11,8 @@
         WindowStartupLocation="CenterOwner"
         Background="{DynamicResource SurfaceBrush}"
         WindowDecorations="BorderOnly"
-        ExtendClientAreaToDecorationsHint="True">
+        ExtendClientAreaToDecorationsHint="True"
+        ExtendClientAreaTitleBarHeightHint="-1">
 
   <Window.Resources>
     <converters:WorktreeStateColorConverter x:Key="WorktreeStateColor"/>