fix(api): a write that hit a connection failure is still reported, and every failure is reported once

Deep-review round 4, the "one report per failure" contract round 3 introduced.

- `req` marked gateway (502/503/504) and network failures "already reported" because they raise
  the connection notice. But that notice is about connectivity and removes itself on the very next
  answer — which every caller's own resync refetch fetches at once — so a delete that hit a
  keepalive reset flashed the notice and was then reported nowhere, the list still there. Only the
  durable reports (the error dialog, the 401 sign-out) count now; the caller says the action failed.
- A connection notice the user closed swallowed every later one for the rest of the visit; it is
  raised again.
- `req` and `uploadReq` share one failure policy (`reportFailure`). The upload copy had drifted: a
  502 opened the blocking "Server error (502)" dialog and cleared a notice that was still true.
- A taken Plex collection name is a structured 409, localized, and the create/rename calls are
  quiet: it was an English dialog plus a Hungarian toast. `notifyCollectionEditError` is gone.
- The mutation onErrors that toasted unconditionally after a non-quiet request (invite approve /
  deny / add, demo whitelist, audit clear, scheduler, share, full history, edit, config tests, tag
  attach) go through `notifyActionError`; the playlist delete's hand-rolled copy of it too (it takes
  a level now). The user role / suspend / delete actions had no onError at all: a user deleted in
  another tab failed silently and stayed listed — now said, and the list refetched.

frontend/src/components/PlexCollectionView.tsx

@@ -5,7 +5,7 @@ import { Play, Shuffle, Pencil, Trash2, Plus, X, Lock, Check, Search } from "luc
 import { qk } from "../lib/queryKeys";
 import { api, isIntrinsicReadOnly, type PlexCard, type PlexCollectionDetail } from "../lib/api";
 import { formatRuntime } from "../lib/format";
-import { notifyActionError, notifyCollectionEditError } from "../lib/actionErrors";
+import { notifyActionError } from "../lib/actionErrors";
 import { notify } from "../lib/notifications";
 import { showEpisodeKeys } from "../lib/plexQueue";
 import { healPlexSort, plexSortOptions } from "../lib/plexSort";
@@ -187,8 +187,8 @@ export default function PlexCollectionView({
       invalidate();
       setRenaming(false);
     } catch (e) {
-      // The backend enforces per-library name uniqueness — localize its 409 to nameTaken.
-      notifyCollectionEditError(e, t("plex.collection.editFailed"), t("plex.collection.nameTaken"));
+      // The backend enforces per-library name uniqueness — a taken name comes back localized.
+      notifyActionError(e, t("plex.collection.editFailed"));
     } finally {
       setBusy(false);
     }