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/Scheduler.tsx

@@ -390,6 +390,7 @@ export default function Scheduler() {
   // live poll surfaces the "running" state within a tick, so we just nudge a refetch.
   const runMut = useMutation({
     mutationFn: (jobId: string) => api.runSchedulerJob(jobId),
+    meta: { failTitle: "errors.writeFailed.schedulerRun" },
     onSuccess: (_d, jobId) => {
       notify({
         level: "success",
@@ -400,6 +401,7 @@ export default function Scheduler() {
   });
   const runAllMut = useMutation({
     mutationFn: () => api.runAllSchedulerJobs(),
+    meta: { failTitle: "errors.writeFailed.schedulerRunAll" },
     onSuccess: (res) => {
       notify({
         level: "success",
@@ -410,10 +412,12 @@ export default function Scheduler() {
   });
   const batchMut = useMutation({
     mutationFn: (v: number) => api.updateMaintenanceBatch(v),
+    meta: { failTitle: "errors.writeFailed.maintenanceBatch" },
     onSuccess: () => qc.invalidateQueries({ queryKey: qk.scheduler() }),
   });
   const purgeMut = useMutation({
     mutationFn: () => api.purgeDiscovery(),
+    meta: { failTitle: "errors.writeFailed.purgeDiscovery" },
     onSuccess: (res) => {
       const removed =
         (res.search_videos_deleted ?? 0) + (res.videos_deleted ?? 0) + (res.channels_deleted ?? 0);