chore(downloads-ui): FE-C4 follow-up cleanup

- Delete dead top-level downloads.rename.* i18n block (en/hu/de); the
  metadata modal moved to downloads.edit.*. Keep downloads.actions.rename
  (still used by ProfileEditor).
- Rename misnamed state renameJob/setRenameJob -> metaJob/setMetaJob in
  DownloadCenter (it opens MetaEditModal, not a rename dialog).
- Extract the duplicated [downloads]/[download-index]/[download-usage]
  invalidation trio into lib/downloads.ts invalidateDownloads(qc);
  used by DownloadCenter and DownloadDialog.

Behavior-neutral. tsc green, knip shows no new unused export, JSON valid.

frontend/src/components/DownloadDialog.tsx

@@ -3,6 +3,7 @@ import { useTranslation } from "react-i18next";
 import { useQuery, useQueryClient } from "@tanstack/react-query";
 import Modal from "./Modal";
 import { api } from "../lib/api";
+import { invalidateDownloads } from "../lib/downloads";
 
 // Lazy: the full profile editor only opens from the dialog's "manage presets" affordance.
 const ProfileEditor = lazy(() => import("./ProfileEditor"));
@@ -43,9 +44,7 @@ export default function DownloadDialog({
         profile_id: chosen,
         display_name: name.trim() || undefined,
       });
-      qc.invalidateQueries({ queryKey: ["downloads"] });
-      qc.invalidateQueries({ queryKey: ["download-index"] });
-      qc.invalidateQueries({ queryKey: ["download-usage"] });
+      invalidateDownloads(qc);
       notify({
         level: "success",
         message: t("downloads.dialog.added"),