feat: add portfolio item symbol to v1 responses

tests/test_v1_portfolios_list.py

@@ -142,6 +142,7 @@ def test_get_service_token_daemon_bound_returns_own_portfolios() -> None:
     data = resp.json()
     assert data["total"] == 1
     assert data["portfolios"][0]["portfolio_id"] == "p-001"
+    assert data["portfolios"][0]["symbol"] == "005930"
 
 
 def test_get_service_token_no_daemon_returns_403() -> None:
@@ -272,3 +273,4 @@ def test_get_response_has_asset_id_field() -> None:
     assert resp.status_code == 200
     item = resp.json()["portfolios"][0]
     assert item["asset_id"] == _ASSET_UUID
+    assert item["symbol"] == "005930"