feat: relocate import tools into studio and harden catalog/furnidata integrity

- Move /admin/import/* tools under /admin/studio/* and add studio nav, layout and tabs
- Add shared catalog maintenance panel plus a /admin/studio/maintenance tab
- Make furnidata reconciliation overwrite conflicting entries with the
  DB-authoritative items_base classname/id (surfaced via fixedConflicts)
- Add furnidata_translate_enabled setting to skip the heavy localized
  furnidata build during import (manual build-languages still forces it)
- Update staff smoke contract test for the studio hub

src/app/admin/studio/maintenance/page.tsx

@@ -0,0 +1,9 @@
+import { CatalogMaintenancePanel } from "@/components/admin/catalog/catalog-maintenance-panel";
+
+export default function StudioCatalogMaintenancePage() {
+	return (
+		<div className="min-h-0">
+			<CatalogMaintenancePanel />
+		</div>
+	);
+}