Fix validation parity regressions

docs/validation-parity-checklist.md

@@ -13,6 +13,7 @@ validation framework, state-management mechanism, or dependency.
 
 - Request validation failures use HTTP 400 and
   `{ "code": "validation_failed", "errors": [{ "field": "...", "code": "..." }] }`.
+- Other safely rejected requests use the stable HTTP 400 code `invalid_request`.
 - Conflicts use HTTP 409, oversized uploads use HTTP 413, unavailable IRL data uses HTTP 503,
   and unexpected failures use HTTP 500. HTTP 422 is not part of this contract.
 - Angular maps known field/code pairs to French inline guidance. Unknown fields/codes, network
@@ -317,7 +318,7 @@ creation, rent-payment recording, and the native condition-photo control.
 Local verification recorded on 2026-07-26:
 
 - Prettier passed for every frontend/documentation file changed since the epic baseline.
-- Frontend lint, application/e2e type checking, production build, and all 327 unit tests passed.
+- Frontend lint, application/e2e type checking, production build, and all 330 unit tests passed.
 - All 36 Playwright journeys passed across mobile, tablet, and desktop viewports.
-- `./mvnw spotless:check verify` passed: 415 unit/web tests, 16 Docker-backed integration tests,
+- `./mvnw spotless:check verify` passed: 416 unit/web tests, 16 Docker-backed integration tests,
   packaging, and coverage checks.