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.ts

@@ -4,6 +4,14 @@ import { qk } from "./queryKeys";
 import { api } from "./api";
 import type { Me } from "./api/account";
 import { readAccount, writeAccount } from "./storage";
+import { notifyActionError } from "./actionErrors";
+import i18n from "../i18n";
+
+// The local state + cache already show the new value, so a refused save is otherwise invisible until
+// the next load quietly puts the old one back. `req` reports none of 403/404/429 and only the
+// connection notice for a lost connection — say it (E11 S2b).
+const reportPrefSaveFailure = (err: unknown) =>
+  notifyActionError(err, i18n.t("errors.writeFailed.prefs"));
 
 // The ONE per-account + server preference hook. A preference (unlike an ephemeral filter) persists to
 // the account on the server (PUT /api/me/preferences, which MERGES the partial payload) AND is adopted
@@ -55,7 +63,7 @@ export function useSavePref(): (patch: Record<string, unknown>) => void {
   const qc = useQueryClient();
   return useCallback(
     (patch: Record<string, unknown>) => {
-      api.savePrefs(patch).catch(() => {});
+      api.savePrefs(patch).catch(reportPrefSaveFailure);
       mergePrefsCache(qc, patch);
     },
     [qc],
@@ -116,9 +124,9 @@ export function usePref<T>(
       // see the new value without a refetch. Merges into preferences, mirroring the server PUT.
       const payload = { [serverKey]: next };
       mergePrefsCache(qc, payload);
-      // savePrefs is fire-and-forget: api.req() already surfaces a failure toast, and the local state +
-      // cache already reflect the change (idempotent PUT retries a transient blip).
-      const flush = () => api.savePrefs(payload).catch(() => {});
+      // savePrefs is fire-and-forget (idempotent PUT, so `req` retries a transient blip once); a
+      // failure that survives that is reported, not swallowed.
+      const flush = () => api.savePrefs(payload).catch(reportPrefSaveFailure);
       if (debounceMs) {
         window.clearTimeout(saveTimer.current);
         pendingSave.current = flush;