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/components/Channels.tsx

@@ -6,7 +6,6 @@ import { Ban, Eye, EyeOff, History, LayoutGrid, Pencil, RefreshCw, Table, X } fr
 import ExcludedChannelList from "./ExcludedChannelList";
 import { api, NO_TAG_SENTINEL, type ManagedChannel } from "../lib/api";
 import { Sparkles } from "lucide-react";
-import { notifyActionError } from "../lib/actionErrors";
 import { notifyYouTubeActionError } from "../lib/youtubeErrors";
 import { accountKey, LS } from "../lib/storage";
 import { buildChannelColumns, applySyncFilter } from "./channelColumns";
@@ -110,6 +109,7 @@ export default function Channels() {
   const [tagManagerOpen, setTagManagerOpen] = useState(false);
   const unblock = useMutation({
     mutationFn: (id: string) => api.unblockChannel(id),
+    meta: { failTitle: "errors.writeFailed.unblockChannel" },
     onSuccess: () => {
       qc.invalidateQueries({ queryKey: qk.blockedChannels() });
       qc.invalidateQueries({ queryKey: qk.feed() });
@@ -133,6 +133,7 @@ export default function Channels() {
       id: string;
       body: { priority?: number; hidden?: boolean; deep_requested?: boolean };
     }) => api.updateChannel(v.id, v.body),
+    meta: { failTitle: "errors.writeFailed.channelSettings" },
     // Requesting full history may have just pulled in a channel's recent uploads, so
     // refresh the per-user status and feed too — not only the channel list.
     onSuccess: () => {
@@ -182,11 +183,10 @@ export default function Channels() {
     // A failed attach/detach reverts the optimistic change by refetching the list. Also refetch
     // suggestions: acceptSuggestion optimistically dropped the channel from that cache, and on
     // failure the tag never actually attached — so the server still suggests it and the ghost chips
-    // must come back rather than leaving an empty cell (honest states). Surface the write failure too.
-    onError: (e) => {
+    // must come back rather than leaving an empty cell (honest states). The hook reports the failure.
+    onError: () => {
       qc.invalidateQueries({ queryKey: qk.channels() });
       qc.invalidateQueries({ queryKey: qk.tagSuggestions() });
-      notifyActionError(e, t("channels.tags.updateFailed"));
     },
   });
   // --- Suggested tags (E8·S4): learned from the user's own manual-tag pattern, shown as accept/dismiss