Address PR #215 review: temporary notes hardening

Must-fix:
- CHANGELOG: add [Unreleased]/Added entry for temporary notes (#201).
- temporary-note-cleanup: re-check temporary_expires_at at deletion time so a
  concurrent "Make permanent" (sets it NULL) between the batch SELECT and the
  per-row removePage wins the race and the note is not trashed. Add unit tests
  for the make-permanent and already-trashed race windows.

Non-blocking review items:
- temporary-note-cleanup: cap the sweep batch (LIMIT 500) so a large backlog is
  not loaded into memory; remainder drains on the next hourly run.
- client: extract duplicated post-toggle cache sync into
  syncTemporaryExpiresInCache() shared by the header menu and the banner.
- Remove the tautological migration spec that mocked the whole Kysely builder.
- Tests: cover create() frozen temporaryExpiresAt (workspace override + NULL
  default fallback + non-temporary skips lookup) and restorePage disarming the
  timer (temporaryExpiresAt: null).

Deferred (forward-looking, non-blocking): extract
PageService.computeTemporaryExpiresAt() to dedupe the deadline formula and drop
the @InjectKysely from PageTemplateController; replace migration unit test with
a real Postgres up/down integration test.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

apps/client/src/features/page/components/header/page-header-menu.tsx

@@ -25,8 +25,10 @@ import { useDisclosure, useHotkeys } from "@mantine/hooks";
 import { useClipboard } from "@/hooks/use-clipboard";
 import { useParams } from "react-router-dom";
 import { usePageQuery } from "@/features/page/queries/page-query.ts";
-import { useToggleTemporaryMutation } from "@/features/page-embed/queries/page-embed-query.ts";
-import { queryClient } from "@/main.tsx";
+import {
+  useToggleTemporaryMutation,
+  syncTemporaryExpiresInCache,
+} from "@/features/page-embed/queries/page-embed-query.ts";
 import { buildPageUrl } from "@/features/page/page.utils.ts";
 import { notifications } from "@mantine/notifications";
 import { getAppUrl } from "@/lib/config.ts";
@@ -176,19 +178,7 @@ function PageActionMenu({ readOnly }: PageActionMenuProps) {
       });
       // Reflect the new deadline in the page cache so the menu label flips and
       // any banner updates. The sidebar icon refreshes via its own query.
-      for (const key of [page.slugId, page.id]) {
-        const cached = queryClient.getQueryData<any>(["pages", key]);
-        if (cached) {
-          queryClient.setQueryData(["pages", key], {
-            ...cached,
-            temporaryExpiresAt: res.temporaryExpiresAt,
-          });
-        }
-      }
-      queryClient.invalidateQueries({
-        predicate: (item) =>
-          ["sidebar-pages"].includes(item.queryKey[0] as string),
-      });
+      syncTemporaryExpiresInCache(page, res.temporaryExpiresAt);
       notifications.show({
         message: next
           ? t("Note will move to trash unless made permanent")