feat(tree): Expand all / Collapse all for the space page tree

Adds a server-authoritative whole-tree endpoint and sidebar menu commands
so a deep space tree can be expanded in one request instead of a per-level
BFS storm.

Server:
- POST /pages/tree (SidebarPageTreeDto: spaceId | pageId), same CASL space
  scoping as /sidebar-pages. Returns the whole space tree / subtree as a flat
  list in the sidebar item shape (id, slugId, title, icon, position,
  parentPageId, spaceId, hasChildren, canEdit), ordered by position
  (collate C byte order), content never fetched.
- page.service.getSidebarPagesTree reproduces getSidebarPages' two-branch
  permission model: open space -> spaceCanEdit; restricted space -> seed the
  full descendant set then prune via filterAccessibleTreePages +
  filterAccessiblePageIdsWithPermissions (keeps restricted-but-granted pages,
  prunes inaccessible subtrees). hasChildren is derived from the final
  filtered set so it can never reveal inaccessible children.
- page.repo.getSpaceDescendants: recursive CTE seeded by space roots.

Client:
- SpaceTree is forwardRef exposing expandAll/collapseAll/isExpanding;
  expandAll fetches the whole tree once, replaces current-space nodes, opens
  every branch (current space only), aborts on space switch, surfaces real
  errors; collapseAll collapses only current-space ids (shared open-map).
- SpaceMenu gains Expand all / Collapse all items (no admin gate).

Implements docs/backlog/tree-expand-collapse-all.md.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

apps/client/public/locales/en-US/translation.json

@@ -977,6 +977,9 @@
   "Page menu": "Page menu",
   "Expand": "Expand",
   "Collapse": "Collapse",
+  "Expand all": "Expand all",
+  "Collapse all": "Collapse all",
+  "Couldn't expand the tree: {{reason}}": "Couldn't expand the tree: {{reason}}",
   "Comment menu": "Comment menu",
   "Group menu": "Group menu",
   "Show hidden breadcrumbs": "Show hidden breadcrumbs",