feat(domain): ProvideDocuments stores the diploma via the ACL then completes the wait (refs #103)

IAclClient.StoreDiplomaAsync + AclHttpClient (base64 JSON to the ACL /documenten
endpoint). ProvideDocuments stores the uploaded bytes against the zaak (when opened)
before completing WachtOpDocumenten; the domain endpoint accepts the file base64-encoded.

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

tests/acceptance/Support/InMemoryZaakGateway.cs

@@ -27,4 +27,7 @@ public sealed class InMemoryZaakGateway : IZaakGateway
 
     public Task<string> GetZaakIdentificatieAsync(Uri zaakUrl, CancellationToken ct = default)
         => Task.FromResult("ACC-REF-1");
+
+    public Task<Uri> StoreDocumentAsync(DocumentRequest request, CancellationToken ct = default)
+        => Task.FromResult(new Uri("http://openzaak/documenten/api/v1/enkelvoudiginformatieobjecten/acc-doc"));
 }