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.Data/Migrations/ClaudeDoDbContextModelSnapshot.cs

@@ -140,12 +140,21 @@ namespace ClaudeDo.Data.Migrations
                         .HasColumnType("TEXT")
                         .HasColumnName("name");
 
+                    b.Property<int>("SortOrder")
+                        .ValueGeneratedOnAdd()
+                        .HasColumnType("INTEGER")
+                        .HasDefaultValue(0)
+                        .HasColumnName("sort_order");
+
                     b.Property<string>("WorkingDir")
                         .HasColumnType("TEXT")
                         .HasColumnName("working_dir");
 
                     b.HasKey("Id");
 
+                    b.HasIndex("SortOrder")
+                        .HasDatabaseName("idx_lists_sort");
+
                     b.ToTable("lists", (string)null);
                 });