fix(#344 review F1-F4): test-mock coverage + getSpaces freshness + comment/test fixes

- F1 [blocking]: share-modal.test.tsx + comment-content-view.test.tsx mocked
  page-query without usePageMetaQuery → 3 tests threw (ShareModal uses it
  directly, comment-content-view via MentionContent). Added usePageMetaQuery to
  both mocks (the space-tree mocks were already fixed; these two were missed).
- F2: restored refetchOnMount:true on useGetSpacesQuery — ["spaces"] is
  invalidated only by same-tab mutations (no socket path), so a cross-actor
  change (an admin adding/removing THIS user from a space) left the list stale
  until a hard reload. The other refetchOnMount removals (favorites/watched —
  per-user, same-tab-only gap) stay removed.
- F3: corrected the trash-list + recent-changes KEEP comments — both keys ARE
  invalidated (trash-list by 3 mutations, recent-changes by page CRUD), but
  invalidateQueries only marks an UNMOUNTED query stale without refetching, so the
  mount refetch closes the gap. The old "never invalidated" wording was wrong and
  risked a maintainer deleting a live invalidation as dead code.
- F4: tests for the two load-bearing pure paths — invalidate-on-update-page (the
  undefined-guard: a title-only event keeps the icon; sibling/unrelated subtrees
  untouched) and breadcrumb-path-equal (equal chain → true; any id/slugId/name/
  icon change or length diff → false; both-null → true). Exported
  breadcrumbPathEqual for the test.

Gate: client tsc 0; the 4 affected/new test files 33 passed.

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

apps/client/src/features/share/components/share-modal.test.tsx

@@ -28,6 +28,7 @@ vi.mock("@/features/share/queries/share-query.ts", () => ({
 
 vi.mock("@/features/page/queries/page-query.ts", () => ({
   usePageQuery: () => ({ data: { id: "page-1", title: "Doc" } }),
+  usePageMetaQuery: () => ({ data: { id: "page-1", title: "Doc" } }),
 }));
 
 vi.mock("@/features/space/queries/space-query.ts", () => ({