test(concepts): add levered_irr keys to FinancialModel contract-key assertion

test_concepts_response_matches_contract_keys pins the exact financial key
set; the two additive levered IRR fields broke it (full-suite-only test,
outside test_financial_dcf.py). Refs #1881

backend/tests/services/generative/test_api_concepts.py

@@ -175,6 +175,9 @@ def test_concepts_response_matches_contract_keys() -> None:
         "total_interest_rub",
         "net_profit_after_financing_rub",
         "financing_is_simplified",
+        # levered (equity) IRR
+        "levered_irr",
+        "levered_irr_is_proxy",
         # price calibration (PR-2)
         "price_per_sqm_used",
         "price_is_calibrated",