feat(portal-openbaar): surface the citizen reference in the public register (refs #78)

The BFF's public view exposes id/status/reference (never bsn/naam) and searches by
id or reference; the openbaar register's Referentie column and search now show the
reference the citizen saw on submit. api-client + openapi.json regenerated.

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

libs/api-client/src/lib/generated/bff-api.ts

@@ -27,6 +27,8 @@ import {
 export interface OpenbaarEntry {
   id: string;
   status: string;
+  /** @nullable */
+  reference: string | null;
 }
 
 export interface SubmitAccepted {