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/import/furni/upload/page.tsx

@@ -1,26 +0,0 @@
-import { redirect } from "next/navigation";
-import { canAccess, getAdminContext, PERMS } from "@/lib/permissions";
-import { UploadFurniClient } from "./upload-furni-client";
-
-export default async function UploadFurniPage() {
-	const { session, permissions } = await getAdminContext();
-	if (!canAccess(permissions, PERMS.ASSETS_IMPORT, session.user.rank)) {
-		redirect("/admin");
-	}
-
-	return (
-		<div className="space-y-6">
-			<div>
-				<h1 className="text-2xl font-bold tracking-tight">
-					Upload .nitro Furniture
-				</h1>
-				<p className="text-muted-foreground mt-1">
-					Upload a .nitro bundle and optional icon to import furniture into the
-					hotel. The database entry, catalog item, and FurnitureData.json will
-					be updated automatically.
-				</p>
-			</div>
-			<UploadFurniClient />
-		</div>
-	);
-}