feat(acl): write the INGEDIEND record on submit and read records back (refs #153)

- OpenZaakAsync upserts a RegisterRecord with status INGEDIEND after opening the zaak,
  keyed on the same zaak id approval later upserts to INGESCHREVEN. The reference comes
  from the registration, so this path needs no ZGW read-back.
- ObjectenGateway.GetAsync fetches an object by the URL a notification carried — no
  objecttype resolution, no search — and reads 404 as "no record" rather than an error.
- POST /register-records/read exposes it to the Event Subscriber, which may not talk to
  Objecten itself (§8.1).

services/acl/Acl.Application/AclService.cs

@@ -24,7 +24,16 @@ public sealed class AclService(
             clock.Today,
             registration.Reference);
 
-        return await gateway.OpenZaakAsync(request, ct);
+        var zaakUrl = await gateway.OpenZaakAsync(request, ct);
+
+        // The register — not ZGW — is what the read projection is sourced from (ADR-0028/ADR-0030),
+        // so the record exists from submission, not only from approval. Same two-writes-converging
+        // posture as ApproveZaakAsync: the upsert is keyed on the zaak id, so a retried submit
+        // updates the record rather than adding a second one (§8.6).
+        await register.UpsertAsync(
+            new RegisterRecord(ZaakId(zaakUrl), RegisterRecordStatus.Ingediend, registration.Reference), ct);
+
+        return zaakUrl;
     }
 
     /// <summary>