refactor: address /code-review on R11 feedback symmetry

- admin._decide: add an idempotency guard (409 unless status was 'pending') so a
  repeat/stale approve OR deny can't re-run its side effects — now that deny emails,
  this stops duplicate denial mails and a rejection mail to an already-approved user.
- SavedViewsWidget: extract runViewMutation(fn, failMsg) (returns success) — dedups
  the five try/catch+refresh blocks AND lets create/rename close their input only on
  success, so a failed create keeps the user's typed name.
- worker._notify_download_done: take user_id/title captured BEFORE the caller's commit
  (no post-commit refresh SELECT); add a  so the inbox labels an edit job
  'Edit ready' instead of 'Download ready' (new inbox.editDone i18n, HU+EN).

Gate green (ruff/tsc/eslint-0/prettier/knip/vitest 79/pytest 193); smoke-tested the
saved-views + notifications surfaces render clean on a fresh dev server.

backend/app/routes/admin.py

@@ -74,6 +74,12 @@ def _decide(db: Session, invite_id: int, admin: User, approved: bool) -> Invite:
     inv = db.get(Invite, invite_id)
     if inv is None:
         raise HTTPException(status_code=404, detail="No such invite")
+    # Idempotency guard: only a still-pending invite can be decided. Without this a repeat/stale
+    # approve or deny re-runs its side effects — re-activating a user, or (now that deny emails)
+    # sending a duplicate decision mail, even flipping an already-approved invite to "denied" and
+    # mailing a rejection to an already-active account.
+    if inv.status != "pending":
+        raise HTTPException(status_code=409, detail="Invite already decided")
     inv.status = "approved" if approved else "denied"
     inv.decided_at = datetime.now(timezone.utc)
     inv.decided_by = admin.email