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/queryClient.ts

@@ -0,0 +1,42 @@
+import { MutationCache, QueryClient } from "@tanstack/react-query";
+import i18n from "../i18n";
+import { notifyActionError } from "./actionErrors";
+
+declare module "@tanstack/react-query" {
+  interface Register {
+    mutationMeta: {
+      /** i18n key of the toast title that names what failed ("Couldn't hide the channel"). Without
+       *  one the failure is still reported, under the generic "Couldn't complete that". */
+      failTitle?: string;
+      /** The component renders this mutation's failure on the page itself — no toast. */
+      errorShownInline?: boolean;
+    };
+  }
+}
+
+type FailMeta = { failTitle?: string; errorShownInline?: boolean } | undefined;
+
+/**
+ * The ONE reporter for a failed mutation. `req` shows its blocking dialog for 400/409/422/5xx only;
+ * a 403/404/429 was left to the caller and a 502–504 or network failure got just the connection
+ * notice — so every `useMutation` without a reporting `onError` failed in silence: a channel hide
+ * that snapped back, a share link that never revoked, a scheduler run that never started (E11 S2b
+ * counted 34 such mutations). Reporting centrally means a new mutation cannot be silent.
+ *
+ * react-query awaits this BEFORE the mutation's own `onError`, so it waits a task: a site that
+ * reported the failure itself (through `notifyActionError`, which marks it) has had its turn, and
+ * `notifyActionError` skips what is already on screen.
+ */
+function reportMutationFailure(err: unknown, meta: FailMeta): void {
+  if (meta?.errorShownInline) return;
+  setTimeout(() => notifyActionError(err, i18n.t(meta?.failTitle ?? "errors.title")), 0);
+}
+
+export function createQueryClient(): QueryClient {
+  return new QueryClient({
+    mutationCache: new MutationCache({
+      onError: (err, _vars, _onMutateResult, mutation) => reportMutationFailure(err, mutation.meta),
+    }),
+    defaultOptions: { queries: { retry: false, staleTime: 30_000, refetchOnWindowFocus: false } },
+  });
+}