feat(portfolios): allow unassigned strategy creation

tests/test_v1_portfolios_crud.py

@@ -507,7 +507,7 @@ def test_delete_already_disabled_is_idempotent() -> None:
 
 
 # Issue #26: strategy catalog references on portfolio mutations.
-def test_post_strategy_reference_errors_and_required_contract() -> None:
+def test_post_strategy_reference_errors_and_optional_contract() -> None:
     repo = _FakeRepo(asset=_make_asset(_ASSET_UUID, "active"))
     client = _make_client()
     with _with_repo(repo):
@@ -516,7 +516,7 @@ def test_post_strategy_reference_errors_and_required_contract() -> None:
             json={"asset_id": _ASSET_UUID, "broker": "kiwoom", "strategy_id": "missing"},
             headers=_auth("admin-tok"),
         )
-        invalid = client.post(
+        without_strategy = client.post(
             "/v1/portfolios",
             json={"asset_id": _ASSET_UUID, "broker": "kiwoom"},
             headers=_auth("admin-tok"),
@@ -528,7 +528,8 @@ def test_post_strategy_reference_errors_and_required_contract() -> None:
             headers=_auth("admin-tok"),
         )
     assert missing.status_code == 404
-    assert invalid.status_code == 422
+    assert without_strategy.status_code == 201
+    assert without_strategy.json()["active_strategy_id"] is None
     assert inactive.status_code == 409