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/Islands/ListsIslandView.axaml

@@ -113,8 +113,18 @@
         <ItemsControl ItemsSource="{Binding UserLists}">
           <ItemsControl.ItemTemplate>
             <DataTemplate DataType="vm:ListNavItemViewModel">
-              <Border Classes="list-item" Classes.active="{Binding IsActive}"
-                      Tapped="OnItemTapped">
+              <Grid RowDefinitions="Auto,Auto,Auto">
+
+                <!-- Above-row drop indicator -->
+                <Border Grid.Row="0" Height="2" VerticalAlignment="Center" Margin="4,0"
+                        Background="{DynamicResource MossBrush}" CornerRadius="1"
+                        IsVisible="{Binding DropHintAbove}"/>
+
+              <Border Grid.Row="1" Classes="list-item" Classes.active="{Binding IsActive}"
+                      Tapped="OnItemTapped"
+                      DragDrop.AllowDrop="True"
+                      DragDrop.DragOver="OnListDragOver"
+                      DragDrop.Drop="OnListDrop">
                 <Border.ContextMenu>
                   <ContextMenu>
                     <MenuItem Header="Settings..."
@@ -123,6 +133,15 @@
                     <MenuItem Header="Worktrees…"
                               Command="{Binding $parent[UserControl].((vm:ListsIslandViewModel)DataContext).OpenWorktreesOverviewCommand}"
                               CommandParameter="{Binding}"/>
+                    <Separator IsVisible="{Binding WorkingDir, Converter={x:Static StringConverters.IsNotNullOrEmpty}}"/>
+                    <MenuItem Header="Open in Explorer"
+                              IsVisible="{Binding WorkingDir, Converter={x:Static StringConverters.IsNotNullOrEmpty}}"
+                              Command="{Binding $parent[UserControl].((vm:ListsIslandViewModel)DataContext).OpenInExplorerCommand}"
+                              CommandParameter="{Binding}"/>
+                    <MenuItem Header="Open in Terminal"
+                              IsVisible="{Binding WorkingDir, Converter={x:Static StringConverters.IsNotNullOrEmpty}}"
+                              Command="{Binding $parent[UserControl].((vm:ListsIslandViewModel)DataContext).OpenInTerminalCommand}"
+                              CommandParameter="{Binding}"/>
                   </ContextMenu>
                 </Border.ContextMenu>
                 <Grid ColumnDefinitions="20,*,Auto">
@@ -152,6 +171,12 @@
                              Text="{Binding Count}"/>
                 </Grid>
               </Border>
+
+                <!-- Below-row drop indicator (last item only) -->
+                <Border Grid.Row="2" Height="2" VerticalAlignment="Center" Margin="4,0"
+                        Background="{DynamicResource MossBrush}" CornerRadius="1"
+                        IsVisible="{Binding DropHintBelow}"/>
+              </Grid>
             </DataTemplate>
           </ItemsControl.ItemTemplate>
         </ItemsControl>