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/useChannelPriority.ts

@@ -1,5 +1,7 @@
 import { useCallback, useEffect, useRef } from "react";
 import { api } from "./api";
+import { notifyActionError } from "./actionErrors";
+import i18n from "../i18n";
 
 /** The shared feed-priority flow used by both the channel manager and the channel detail page:
  *  an optimistic bump/set with a debounced server flush (~400ms after the last notch) so a
@@ -34,7 +36,12 @@ export function useChannelPriority(opts: {
     api
       .updateChannel(channelId, { priority: latest })
       .then(() => optsRef.current.onSuccess?.(channelId))
-      .catch(() => optsRef.current.onError(channelId));
+      .catch((err: unknown) => {
+        // Said here, once, for both callers: their `onError` only refetches, so a refused priority
+        // used to just snap back — often after the stepper had already been let go (E11 S2b).
+        notifyActionError(err, i18n.t("errors.writeFailed.channelPriority"));
+        optsRef.current.onError(channelId);
+      });
   }, []);
 
   // Set an absolute priority (used by both the arrows — via bumpPriority — and the inline edit),