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/PlexCollectionEditor.tsx

@@ -4,7 +4,7 @@ import { useTranslation } from "react-i18next";
 import { useQuery, useQueryClient } from "@tanstack/react-query";
 import { Check, Plus } from "lucide-react";
 import { api } from "../lib/api";
-import { notifyCollectionEditError } from "../lib/actionErrors";
+import { notifyActionError } from "../lib/actionErrors";
 import { useScrollFade } from "../lib/useScrollFade";
 import { Button } from "./ui/Button";
 import Modal from "./ui/Modal";
@@ -103,9 +103,9 @@ export default function PlexCollectionEditor({
       setMembers((prev) => new Set(prev).add(col.id));
       refresh();
     } catch (e) {
-      // The backend rejects a duplicate name with 409 (Plex conflates same names) — localize it to
-      // nameTaken rather than surfacing the server's raw English detail.
-      notifyCollectionEditError(e, t("plex.collection.editFailed"), t("plex.collection.nameTaken"));
+      // The backend rejects a duplicate name with 409 (Plex conflates same names), structured — so
+      // it reads in the reader's language (see localizeDetail).
+      notifyActionError(e, t("plex.collection.editFailed"));
     } finally {
       setBusy(null);
     }