feat(acl): store a diploma in the Documenten API and relate it to the zaak (refs #103)

IZaakGateway.StoreDocumentAsync creates an enkelvoudiginformatieobject (base64
inhoud, buffered non-chunked body, no CRS) and relates it via zaakinformatieobjecten;
AclService.StoreDiplomaAsync default-fills the ZGW document fields (informatieobjecttype,
bronorganisatie, taal nld, creatiedatum); POST /documenten exposes it. Adds the
InformatieobjecttypeUrl default (wired in a following infra commit).

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

services/acl/Acl.Tests/AclServiceTests.cs

@@ -30,6 +30,15 @@ public class AclServiceTests
             ReadReferenceFor = zaakUrl;
             return Task.FromResult("REG-FROM-ZAAK");
         }
+
+        public DocumentRequest? StoredDocument;
+        public Uri DocumentResult { get; } = new("http://openzaak/documenten/api/v1/enkelvoudiginformatieobjecten/doc-1");
+
+        public Task<Uri> StoreDocumentAsync(DocumentRequest request, CancellationToken ct = default)
+        {
+            StoredDocument = request;
+            return Task.FromResult(DocumentResult);
+        }
     }
 
     private static AclDefaults Defaults() => new()
@@ -38,6 +47,7 @@ public class AclServiceTests
         VerantwoordelijkeOrganisatie = "517439943",
         Vertrouwelijkheidaanduiding = "openbaar",
         ZaaktypeUrl = new("http://openzaak/catalogi/api/v1/zaaktypen/big"),
+        InformatieobjecttypeUrl = new("http://openzaak/catalogi/api/v1/informatieobjecttypen/dip"),
     };
 
     private sealed class FixedClock(DateOnly today) : IClock
@@ -55,6 +65,7 @@ public class AclServiceTests
             VerantwoordelijkeOrganisatie = "517439943",
             Vertrouwelijkheidaanduiding = "openbaar",
             ZaaktypeUrl = new("http://openzaak/catalogi/api/v1/zaaktypen/big"),
+            InformatieobjecttypeUrl = new("http://openzaak/catalogi/api/v1/informatieobjecttypen/dip"),
         };
         var service = new AclService(gateway, defaults, new FixedClock(new DateOnly(2026, 6, 4)));
 
@@ -81,6 +92,7 @@ public class AclServiceTests
             VerantwoordelijkeOrganisatie = "517439943",
             Vertrouwelijkheidaanduiding = "openbaar",
             ZaaktypeUrl = new("http://openzaak/catalogi/api/v1/zaaktypen/big"),
+            InformatieobjecttypeUrl = new("http://openzaak/catalogi/api/v1/informatieobjecttypen/dip"),
         };
         var service = new AclService(gateway, defaults, new FixedClock(new DateOnly(2026, 6, 4)));
 
@@ -114,6 +126,41 @@ public class AclServiceTests
         Assert.Null(gateway.Approved);
     }
 
+    [Fact]
+    public async Task Storing_a_diploma_default_fills_the_document_fields_and_returns_its_url()
+    {
+        var gateway = new FakeGateway();
+        var defaults = Defaults();
+        var service = new AclService(gateway, defaults, new FixedClock(new DateOnly(2026, 6, 4)));
+        var zaak = new Uri("http://openzaak/zaken/api/v1/zaken/abc");
+
+        var url = await service.StoreDiplomaAsync(zaak, [1, 2, 3], "diploma.pdf", "application/pdf");
+
+        Assert.Equal(gateway.DocumentResult, url);
+        var req = gateway.StoredDocument!;
+        Assert.Equal(zaak, req.Zaak);
+        Assert.Equal(defaults.InformatieobjecttypeUrl, req.Informatieobjecttype);
+        Assert.Equal("517439943", req.Bronorganisatie);
+        Assert.Equal("openbaar", req.Vertrouwelijkheidaanduiding);
+        Assert.Equal(new DateOnly(2026, 6, 4), req.Creatiedatum);
+        Assert.Equal("nld", req.Taal);
+        Assert.Equal("diploma.pdf", req.Bestandsnaam);
+        Assert.Equal("application/pdf", req.Formaat);
+        Assert.Equal(new byte[] { 1, 2, 3 }, req.Inhoud);
+    }
+
+    [Fact]
+    public async Task Storing_a_diploma_rejects_null_or_blank_arguments()
+    {
+        var service = new AclService(new FakeGateway(), Defaults(), new FixedClock(new DateOnly(2026, 6, 4)));
+        var zaak = new Uri("http://openzaak/zaken/api/v1/zaken/abc");
+
+        await Assert.ThrowsAsync<ArgumentNullException>(() => service.StoreDiplomaAsync(null!, [1], "d.pdf", "application/pdf"));
+        await Assert.ThrowsAsync<ArgumentNullException>(() => service.StoreDiplomaAsync(zaak, null!, "d.pdf", "application/pdf"));
+        await Assert.ThrowsAnyAsync<ArgumentException>(() => service.StoreDiplomaAsync(zaak, [1], " ", "application/pdf"));
+        await Assert.ThrowsAnyAsync<ArgumentException>(() => service.StoreDiplomaAsync(zaak, [1], "d.pdf", " "));
+    }
+
     [Fact]
     public async Task Reading_a_zaak_reference_returns_the_zaaks_identificatie()
     {