test(api-client): generated BFF client is exposed and calls the endpoints (refs #66)

Scaffold libs/api-client (Nx Angular lib) and generate a typed HttpClient client
from services/bff/openapi.json with orval (node-based; Angular target integrates
with HttpClient interceptors for the S-08c auth token). A failing test drives the
public API: it expects an injectable BffApiV1Service to POST /self-service/registrations
and GET /openbaar/register (via HttpClientTesting), but the lib barrel doesn't export
the client yet, so it fails. Normalise the vitest target to 'test'. Green exposes it.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

package.json

@@ -52,6 +52,7 @@
     "jsdom": "~22.1.0",
     "jsonc-eslint-parser": "^2.1.0",
     "nx": "23.0.1",
+    "orval": "^8.19.0",
     "prettier": "^3.8.1",
     "ts-node": "10.9.1",
     "tslib": "^2.3.0",