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/AdminUsers.tsx

@@ -38,7 +38,7 @@ import { useConfirm } from "./ConfirmProvider";
 import Tabs, { usePersistedTab } from "./ui/Tabs";
 import { PageToolbar } from "./ui/PageShell";
 import { useMe } from "../lib/useMe";
-import { notifyActionError } from "../lib/actionErrors";
+import { notifyActionError, notifyKnownFailure } from "../lib/actionErrors";
 
 // Admin-only user & access management: roles, access requests (the Invite whitelist), and the
 // demo whitelist + reset. Each section is its own tab (persisted across reloads); the Access tab
@@ -351,7 +351,7 @@ function PendingAccess() {
       refresh();
       notify({ level: "success", message: t("users.pendingAccess.activated", { email: u.email }) });
     },
-    onError: () => notify({ level: "error", message: t("users.pendingAccess.activateFailed") }),
+    onError: (err) => notifyActionError(err, t("users.pendingAccess.activateFailed")),
   });
 
   const resend = useMutation({
@@ -363,12 +363,9 @@ function PendingAccess() {
     // The public resend is deliberately silent; this one is not, so say WHY it failed — an instance
     // with no working SMTP would otherwise show a success toast for a mail that was never sent.
     onError: (err) =>
-      notify({
-        level: "error",
-        message: isEmailOff(err)
-          ? t("users.pendingAccess.resendEmailOff")
-          : t("users.pendingAccess.resendFailed"),
-      }),
+      isEmailOff(err)
+        ? notifyKnownFailure(err, t("users.pendingAccess.resendEmailOff"))
+        : notifyActionError(err, t("users.pendingAccess.resendFailed")),
   });
 
   const list = rows.data ?? [];
@@ -563,12 +560,8 @@ function AdminInvites() {
       // A 409 means the list was stale — someone registered on that address since it loaded. Say
       // what to do instead of a generic failure, and refetch so the row re-renders as read-only.
       const conflict = e instanceof HttpError && e.status === 409;
-      notify({
-        level: "error",
-        message: t(
-          conflict ? "settings.invites.deleteHasAccount" : "settings.invites.deleteFailed",
-        ),
-      });
+      if (conflict) notifyKnownFailure(e, t("settings.invites.deleteHasAccount"));
+      else notifyActionError(e, t("settings.invites.deleteFailed"));
       if (conflict) refresh();
     },
   });
@@ -599,13 +592,9 @@ function AdminInvites() {
       notify({ level: "success", message: t("settings.invites.invited", { email: v.inv.email }) });
     },
     onError: (err) =>
-      notify({
-        level: "error",
-        message:
-          err instanceof HttpError && inviteEmailOff(err)
-            ? t("settings.invites.inviteEmailOff")
-            : t("settings.invites.inviteFailed"),
-      }),
+      err instanceof HttpError && inviteEmailOff(err)
+        ? notifyKnownFailure(err, t("settings.invites.inviteEmailOff"))
+        : notifyActionError(err, t("settings.invites.inviteFailed")),
   });
   // The one recipient the app has no language signal about: the admin typed this address in, so
   // nobody ever told us how to write to its owner. The dialog is where that gets decided — and it