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/SettingsModalView.axaml

@@ -7,9 +7,11 @@
         x:Class="ClaudeDo.Ui.Views.Modals.SettingsModalView"
         x:DataType="vm:SettingsModalViewModel"
         Title="Settings"
-        Width="580" Height="760"
-        WindowDecorations="None"
+        Width="580" Height="760" MinWidth="480" MinHeight="520"
+        CanResize="True"
+        WindowDecorations="BorderOnly"
         ExtendClientAreaToDecorationsHint="True"
+        ExtendClientAreaTitleBarHeightHint="-1"
         WindowStartupLocation="CenterOwner"
         Background="{DynamicResource SurfaceBrush}">