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/lib/admin-theme-source-audit.test.ts

@@ -6,7 +6,6 @@ const ROOTS = ["src/app/admin", "src/components/admin"];
 const GRAPHICAL_ALLOWLIST = [
 	"src/app/admin/favicon/favicon-generator.tsx",
 	"src/app/admin/import/clone/import-clone-client.tsx",
-	"src/app/admin/import/furni/import-furni-client.tsx",
 	"src/components/admin/catalog/items-shop-preview.tsx",
 	"src/components/admin/media-grid.tsx",
 ];