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>

services/bff/Bff.Api/OpenbaarProjection.cs

@@ -11,8 +11,10 @@ public static class OpenbaarProjection
     {
         var filtered = string.IsNullOrWhiteSpace(q)
             ? entries
-            : entries.Where(e => e.Id.Contains(q, StringComparison.OrdinalIgnoreCase));
+            : entries.Where(e =>
+                e.Id.Contains(q, StringComparison.OrdinalIgnoreCase) ||
+                (e.Reference?.Contains(q, StringComparison.OrdinalIgnoreCase) ?? false));
 
-        return [.. filtered.Select(e => new OpenbaarEntry(e.Id, e.Status))];
+        return [.. filtered.Select(e => new OpenbaarEntry(e.Id, e.Status, e.Reference))];
     }
 }