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/main.tsx

@@ -1,6 +1,7 @@
 import React, { lazy, Suspense } from "react";
 import { createRoot } from "react-dom/client";
-import { QueryClient, QueryClientProvider } from "@tanstack/react-query";
+import { QueryClientProvider } from "@tanstack/react-query";
+import { createQueryClient } from "./lib/queryClient";
 import { FloatingTree } from "@floating-ui/react";
 import ErrorBoundary from "./components/ErrorBoundary";
 import { ConfirmProvider } from "./components/ConfirmProvider";
@@ -28,9 +29,7 @@ const PrivacyPolicy = lazy(() => import("./components/legal/PrivacyPolicy"));
 const Terms = lazy(() => import("./components/legal/Terms"));
 const WatchPage = lazy(() => import("./components/WatchPage"));
 
-const queryClient = new QueryClient({
-  defaultOptions: { queries: { retry: false, staleTime: 30_000, refetchOnWindowFocus: false } },
-});
+const queryClient = createQueryClient();
 
 // Baseline theme so the token CSS vars (--bg/--surface/--accent/…) resolve on first paint — including
 // the standalone public pages (/watch, /privacy, /terms) that render outside <App> and never call