test(domain): expiry worker cancels the zaak via the ACL on timeout (refs #106)

S-10c: expiring the aggregate to VERLOPEN is not enough — the ZGW zaak must
also be cancelled through the ACL (§8.1). Adds IAclClient.CancelZaakAsync and
its client/fakes, and asserts the worker cancels a still-open registration's
zaak but leaves an already-resolved one untouched.

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

services/domain/Big.Infrastructure/AclHttpClient.cs

@@ -31,6 +31,15 @@ public sealed class AclHttpClient(HttpClient http, AclOptions options) : IAclCli
         response.EnsureSuccessStatusCode();
     }
 
+    public async Task CancelZaakAsync(Uri zaakUrl, CancellationToken ct = default)
+    {
+        ArgumentNullException.ThrowIfNull(zaakUrl);
+
+        using var response = await http.PostAsJsonAsync(
+            new Uri(options.BaseUrl, "annuleringen"), new CancelZaakRequest(zaakUrl.ToString()), ct);
+        response.EnsureSuccessStatusCode();
+    }
+
     public async Task<Uri> StoreDiplomaAsync(Uri zaakUrl, byte[] content, string fileName, string contentType, CancellationToken ct = default)
     {
         ArgumentNullException.ThrowIfNull(zaakUrl);
@@ -56,6 +65,8 @@ public sealed class AclHttpClient(HttpClient http, AclOptions options) : IAclCli
 
     private sealed record SetStatusRequest([property: JsonPropertyName("zaakUrl")] string ZaakUrl);
 
+    private sealed record CancelZaakRequest([property: JsonPropertyName("zaakUrl")] string ZaakUrl);
+
     private sealed record StoreDocumentRequest(
         [property: JsonPropertyName("zaakUrl")] string ZaakUrl,
         [property: JsonPropertyName("contentBase64")] string ContentBase64,