refactor(studio): extract helper components from OrganizeImportsDialog

Extract FurniThumb, LayoutPreview, and GroupItemList into a dedicated
mall-helpers module alongside OrganizeImportsDialog. Preserves all
virtualization, drag-and-drop, and preview behavior while reducing
the main dialog component size.

src/components/admin/catalog/catalog-items-table/catalog-items-table.tsx

@@ -90,12 +90,12 @@ import {
 import { useServerAction } from "@/hooks/use-server-action";
 import { getSuggestions, recordMove } from "@/lib/move-suggestions";
 import { cn } from "@/lib/utils";
+import { AddItemFormFields } from "./add-item-form-fields";
 import {
 	InteractionTypeCombobox,
 	MovePageCombobox,
 	ToggleField,
 } from "./field-helpers";
-import { AddItemFormFields } from "./add-item-form-fields";
 import { FurniIcon } from "./furni-icon";
 import { SongPicker } from "./song-picker";
 import {