fix(ui): a write that fails says what failed and why, wherever it fails

`req` opens its blocking dialog for 400/409/422/5xx only. A 403/404/429 was left to the caller and a
502-504 or lost connection got just the self-clearing connection notice, so 34 mutations without a
reporting onError and 15 direct api writes with a bare or missing catch failed in silence: a hidden
channel that snapped back, a share link that never revoked, a confirmed account delete that ended
with nothing said.

- lib/queryClient: one MutationCache reporter. react-query awaits it BEFORE the mutation's own
  onError, so it waits a task and skips a failure the site already reported; the toast title comes
  from `meta.failTitle`, `meta.errorShownInline` opts out.
- notifyActionError: title names WHAT failed, the line under it says WHY (`failureReason`: a
  structured localized detail, else the status). It marks the error reported (`markReported`), so
  nothing reports one failure twice; `notifyKnownFailure` for a site's own specific sentence.
- Every silent site named (45 new HU/EN titles, 4 reasons). Stale "the global dialog shows it"
  comments corrected on the job actions, channel block, Plex sync, cookies, download enqueue,
  account delete and usePref.
- Channels passed the tag hook's channel id to the reporter as the error; the tag and priority hooks
  now report themselves, with the real error.
- A contract test keeps every useMutation naming its failure; CLAUDE.md gains the pattern row.
- history.dom.test: the "navigates only once the entries are back" assertion raced an async act's
  macrotask flush (1 in 5 runs); it now asserts from a later popstate listener.

frontend/src/lib/usePref.dom.test.ts

@@ -14,7 +14,9 @@ const { store, savePrefs } = vi.hoisted(() => ({
   savePrefs: vi.fn(() => Promise.resolve({})),
 }));
 
-vi.mock("./storage", () => ({
+// Partial: i18n (which usePref now imports, to title a refused save) reads its key from `LS`.
+vi.mock("./storage", async (importOriginal) => ({
+  ...(await importOriginal<typeof import("./storage")>()),
   readAccount: (base: string, fallback: unknown) => {
     const raw = store.get(base);
     return raw == null ? fallback : JSON.parse(raw);
@@ -24,6 +26,9 @@ vi.mock("./storage", () => ({
   },
 }));
 vi.mock("./api", () => ({ api: { savePrefs, me: vi.fn() } }));
+// The failure path (usePref.saveFailure.dom.test.ts) is not this file's subject; stubbed so the
+// reporter's notifications → storage chain does not meet the storage mock above.
+vi.mock("./actionErrors", () => ({ notifyActionError: vi.fn() }));
 
 import { usePref, useSavePref } from "./usePref";
 import { qk } from "./queryKeys";