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/server/src/database/repos/page/page.repo.ts

@@ -672,4 +672,58 @@ export class PageRepo {
         .execute()
     );
   }
+
+  /**
+   * Whole space tree (all root pages and their descendants) in a single
+   * recursive query. Mirrors getPageAndDescendants but seeded by every root
+   * page of the space (parentPageId IS NULL) instead of a single parent.
+   */
+  async getSpaceDescendants(
+    spaceId: string,
+    opts: { includeContent: boolean },
+  ) {
+    return this.db
+      .withRecursive('page_hierarchy', (db) =>
+        db
+          .selectFrom('pages')
+          .select([
+            'id',
+            'slugId',
+            'title',
+            'icon',
+            'position',
+            'parentPageId',
+            'spaceId',
+            'workspaceId',
+            'createdAt',
+            'updatedAt',
+          ])
+          .$if(opts?.includeContent, (qb) => qb.select('content'))
+          .where('spaceId', '=', spaceId)
+          .where('parentPageId', 'is', null)
+          .where('deletedAt', 'is', null)
+          .unionAll((exp) =>
+            exp
+              .selectFrom('pages as p')
+              .select([
+                'p.id',
+                'p.slugId',
+                'p.title',
+                'p.icon',
+                'p.position',
+                'p.parentPageId',
+                'p.spaceId',
+                'p.workspaceId',
+                'p.createdAt',
+                'p.updatedAt',
+              ])
+              .$if(opts?.includeContent, (qb) => qb.select('p.content'))
+              .innerJoin('page_hierarchy as ph', 'p.parentPageId', 'ph.id')
+              .where('p.deletedAt', 'is', null),
+          ),
+      )
+      .selectFrom('page_hierarchy')
+      .selectAll()
+      .execute();
+  }
 }