Preserve ledger venue provenance (#39)

* feat: preserve ledger venue provenance

* fix: satisfy ledger test lint ratchet

* fix: advance image migration inventory

tests/test_v1_portfolios_manual_ledger.py

@@ -1030,6 +1030,8 @@ def test_unified_ledger_includes_corporate_action_fields() -> None:
         "evidence_ref": "notice://ca-7",
         "actor_user_id": _USER_ID,
         "recorded_at": "2026-09-02T00:00:00Z",
+        "execution_venue": None,
+        "order_venue": None,
     }
 
 
@@ -1094,6 +1096,7 @@ def test_unified_ledger_paginates_mixed_sources_and_hides_side() -> None:
         LedgerEntry(
             ledger_entry_id=99, portfolio_id=_PORTFOLIO_ID, side="buy", quantity=2, price=10, source="broker",
             recorded_at=datetime.now(UTC), cash_balance_after=900, asset_quantity_after=12,
+            execution_venue="NXT", order_venue="SOR",
         )
     )
     first = client.get(f"/v1/portfolios/{_PORTFOLIO_ID}/ledger?limit=1", headers=_auth())
@@ -1101,6 +1104,8 @@ def test_unified_ledger_paginates_mixed_sources_and_hides_side() -> None:
     first_item = first.json()["items"][0]
     assert first_item["source"] == "broker"
     assert first_item["action"] == "BUY"
+    assert first_item["execution_venue"] == "NXT"
+    assert first_item["order_venue"] == "SOR"
     assert "side" not in first_item
     assert first.json()["next_cursor"]
     second = client.get(