feat(event-subscriber): enrich the projection with the zaak reference via the ACL (refs #78)

On each notification the subscriber reads the zaak's reference (identificatie)
through the ACL — the only code allowed to talk to ZGW (§8.1) — and persists it on
the register_projection row and in the processed_notifications replay log. Storing
it in the log keeps rebuild log-only (ADR-0008): no ACL/ZGW access on rebuild.

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

services/projection-api/Projection.ReadModel/EfNotificationLog.cs

@@ -16,6 +16,7 @@ public sealed class EfNotificationLog(ProjectionDbContext db) : INotificationLog
             Actie = notification.Actie,
             ZaakId = notification.ZaakId,
             Resource = notification.Resource,
+            Reference = notification.Reference,
             ReceivedAt = DateTimeOffset.UtcNow,
         });
 
@@ -35,6 +36,6 @@ public sealed class EfNotificationLog(ProjectionDbContext db) : INotificationLog
     public async Task<IReadOnlyList<RecordedNotification>> AllAsync(CancellationToken ct = default)
         => await db.ProcessedNotifications
             .OrderBy(r => r.ReceivedAt)
-            .Select(r => new RecordedNotification(r.Key, r.Actie, r.ZaakId, r.Resource))
+            .Select(r => new RecordedNotification(r.Key, r.Actie, r.ZaakId, r.Resource, r.Reference))
             .ToListAsync(ct);
 }