S-09b: Approval flow — temp admin endpoint + status transition to projection (#77)

## What & why

S-09b (#75, split from #10) — the **approval flow** that completes the walking skeleton. A behandelaar can now approve a submitted registration; the entry flips from `INGEDIEND` to `INGESCHREVEN` in the public register. Flow: `POST /registrations/{id}/approve` (domain) → ACL sets the zaak eindstatus (ZGW `/statussen`) → OpenZaak → NRC → event-subscriber → projection → openbaar.

## Changes (bottom-up, each red→green TDD)

- **Domain** — `RegistrationStatus.Ingeschreven` + `Registration.Approve()` (guards: opened zaak, only from INGEDIEND); `ApproveRegistration` use case (idempotent) + temp `POST /registrations/{id}/approve` endpoint; `IAclClient.ApproveZaakAsync`.
- **ACL** — resolves the zaaktype's **eindstatus** from the catalogus (`isEindstatus` / highest volgnummer) and POSTs a ZGW status; exposed as `POST /statussen`. Unit + real-OpenZaak integration test.
- **Event-subscriber** — binds NRC `hoofdObject`, projects a `status`/`create` as `INGESCHREVEN` keyed on the zaak (updates the existing row), **without reading OpenZaak** (§8.1). Retains the ZGW `resource` in the log (new column + EF migration) so a rebuild reproduces the status.
- **e2e** — extended: submit → public INGEDIEND → approve → public INGESCHREVEN.
- **Docs** — ADR-0011 (the two non-obvious decisions + the walking-skeleton assumption) + demo note.

## Key decisions (see ADR-0011)

- **ACL discovers the eindstatus** (chosen over injecting a statustype URL): no new config/seed plumbing, domain stays ZGW-ignorant.
- **Any post-creation status-set ⇒ INGESCHREVEN**: in the walking skeleton the only status ever set after creation is the approval, and the subscriber may not read ZGW — documented to tighten when more transitions arrive (S-12+).

## Verification

- All .NET unit suites green locally (domain 47, acl 11, event-subscriber 14, bff 16, acceptance 7); Release build + `dotnet format` clean.
- No new compose config (the eindstatus-discovery approach avoided it).
- The real-OpenZaak integration test (ACL status-set) and the full submit→approve→visible e2e run in CI `verify-stack` (live NRC→projection + selectielijst egress, not reproducible locally).

closes #75

Reviewed-on: #77

services/acl/Acl.Application/AclService.cs

@@ -17,4 +17,15 @@ public sealed class AclService(IZaakGateway gateway, AclDefaults defaults, ICloc
 
         return gateway.OpenZaakAsync(request, ct);
     }
+
+    /// <summary>
+    /// Approve a zaak: set it to the eindstatus of the configured BIG zaaktype (ADR-0003 default). The
+    /// domain hands over only the zaak URL; the ACL owns which statustype means "approved" (§8.1).
+    /// </summary>
+    public Task ApproveZaakAsync(Uri zaakUrl, CancellationToken ct = default)
+    {
+        ArgumentNullException.ThrowIfNull(zaakUrl);
+
+        return gateway.SetZaakToEindstatusAsync(zaakUrl, defaults.ZaaktypeUrl, clock.Today, ct);
+    }
 }

services/acl/Acl.Application/IZaakGateway.cs

@@ -5,4 +5,11 @@ namespace Acl.Application;
 public interface IZaakGateway
 {
     Task<Uri> OpenZaakAsync(ZaakRequest request, CancellationToken ct = default);
+
+    /// <summary>
+    /// Set the given zaak to the <em>eindstatus</em> (final statustype) of the supplied zaaktype —
+    /// the ZGW translation of "approve". The gateway resolves which statustype is the eindstatus from
+    /// the catalogus and POSTs a status against the zaak, dated <paramref name="datumStatusGezet"/>.
+    /// </summary>
+    Task SetZaakToEindstatusAsync(Uri zaakUrl, Uri zaaktypeUrl, DateOnly datumStatusGezet, CancellationToken ct = default);
 }