fix: tree API 500 — sqlite3.Row doesn't support .get(), use bracket r['key']

sqlite3.Row objects only support __getitem__ (r['key']), not the .get()
method. Changed r.get('parent_section') to r['parent_section'] in
folder type detection logic.

app/routers/dashboard.py

@@ -530,7 +530,7 @@ async def local_workspace_tree(request: Request):
             children = conn.execute(
                 "SELECT id, title, parent_section FROM pages WHERE parent_id=? ORDER BY created_at", (r["id"],)
             ).fetchall()
-        is_folder = r.get("parent_section") == "Workspace"
+        is_folder = r["parent_section"] == "Workspace"
         rtype = "folder" if is_folder else "page"
         item = {"id": r["id"], "name": r["title"] or "Untitled", "type": rtype,
                 "children": [{"id": c["id"], "name": c["title"] or "Untitled", "type": "page"} for c in children]}