feat(api-client): expose the generated BFF client + repeatable generate target (refs #66)

The lib barrel exports the generated BffApiV1Service + models (SubmitAccepted,
OpenbaarEntry), so the app can inject a typed client for the BFF. Add an
'api-client:generate' target (orval) to regenerate from services/bff/openapi.json;
generation is idempotent. Tests (HttpClientTesting) now pass: POST /self-service/
registrations and GET /openbaar/register with the query, mapping typed responses.

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

libs/api-client/project.json

@@ -8,6 +8,13 @@
   "targets": {
     "lint": {
       "executor": "@nx/eslint:lint"
+    },
+    "generate": {
+      "executor": "nx:run-commands",
+      "options": {
+        "command": "orval --config orval.config.ts",
+        "cwd": "libs/api-client"
+      }
     }
   }
 }