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/components/admin/studio/studio-client.tsx

@@ -602,10 +602,7 @@ export function StudioClient({
 	);
 
 	return (
-		<div
-			className="flex h-[calc(100dvh-7rem)] min-h-[520px] flex-col overflow-hidden rounded-xl border border-[var(--admin-border)]"
-			style={{ backgroundColor: "var(--admin-canvas)" }}
-		>
+		<div className="flex h-full min-h-[520px] flex-col overflow-hidden">
 			{/* ── Header ─────────────────────────────────────────── */}
 			<header className="flex shrink-0 flex-wrap items-center gap-3 border-b border-[var(--admin-border)] bg-[var(--admin-surface)] px-4 py-3">
 				<div className="flex items-center gap-2.5">