fix: tree API 500 — missing parent_section in SELECT query

The roots query only had id, title columns but the tree builder
accessed r['parent_section'] which didn't exist in the result row.
Added parent_section to the SELECT to fix folder type detection.

app/routers/dashboard.py

@@ -521,7 +521,7 @@ async def local_workspace_tree(request: Request):
     ws_id = ws["id"] if ws else None
     with get_conn() as conn:
         roots = conn.execute(
-            "SELECT id, title FROM pages WHERE parent_id IS NULL AND workspace_id=? ORDER BY created_at DESC",
+            "SELECT id, title, parent_section FROM pages WHERE parent_id IS NULL AND workspace_id=? ORDER BY created_at DESC",
             (ws_id,),
         ).fetchall() if ws_id else []
     tree = []