feat(acl): diploma upload stored in the ZGW Documenten API (S-10b, closes #103) (#108)

## What & why

S-10b: the self-service **diploma upload** is now real. After submitting, the citizen picks a PDF and
uploads it; the portal base64-encodes it client-side → BFF → domain → **ACL**, which stores it in the
ZGW **Documenten (DRC) API** as an `enkelvoudiginformatieobject` and relates it to the zaak, then the
`WachtOpDocumenten` wait completes and the case advances to beoordeling. Per §8.1 only the ACL talks to
ZGW.

Closes #103

Mechanism in **ADR-0018** (proposal #107). Builds on S-10a (#102). The zaak-close-on-expiry item is
carved to **#106 (S-10c)**.

## Definition of Done

- [x] Linked Gitea issue (above).
- [x] Failing test committed before the implementation (red→green per layer).
- [x] Conventional Commits referencing the issue (`refs #103`).
- [ ] CI green — all Gitea Actions jobs (pending on this PR).
- [x] `docker compose up` health unaffected (ACL boots on a placeholder informatieobjecttype URL; the real one is injected by verify-domain).
- [x] Docs updated (ADR-0018, demo-script, BACKLOG + S-10c).
- [x] ADR added (`docs/architecture/adr-0018-diploma-upload-via-acl-documenten.md`).
- [x] Demo note in `docs/demo-script.md`.

## Notes for reviewers

- **ACL** (`OpenZaakGateway.StoreDocumentAsync` + `AclService.StoreDiplomaAsync` + `POST /documenten`) reuses the existing gateway patterns (ZGW Bearer, buffered non-chunked body, **no CRS** — Documenten isn't geo). Unit-tested via the stub handler; an **integration test** stores a real document against live OpenZaak (verify-acl).
- **Transport:** base64 JSON on every hop (portal encodes client-side) — I deviated from proposal #107's multipart to keep one contract shape and avoid `IFormFile`/antiforgery/multipart-client plumbing; fine at diploma size (ADR-0018 §Alternatives).
- **Infra:** `seed_catalogus.py` seeds + publishes a "Diploma" `informatieobjecttype` and relates it to the zaaktype (while both concept); `verify-domain` injects its URL into the ACL. No new ZGW scopes (seed applicatie has `heeft_alle_autorisaties`).
- **e2e:** uploads a real PDF (`setInputFiles`) after the openbaar INGEDIEND row confirms the zaak is open (so storage doesn't race the OpenZaak worker).
- **Scope boundary:** the ZGW zaak is not set to a cancellation status on 30-day expiry — that's #106 (S-10c).

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Reviewed-on: #108

services/acl/Acl.Infrastructure/OpenZaakGateway.cs

@@ -80,6 +80,39 @@ public sealed class OpenZaakGateway(HttpClient http, OpenZaakOptions options) :
         return zaak.Identificatie;
     }
 
+    public async Task<Uri> StoreDocumentAsync(DocumentRequest request, CancellationToken ct = default)
+    {
+        ArgumentNullException.ThrowIfNull(request);
+
+        // 1. Create the enkelvoudiginformatieobject in the Documenten API (not a geo API — no CRS).
+        var created = await PostForUrlAsync(
+            "/documenten/api/v1/enkelvoudiginformatieobjecten",
+            new EnkelvoudigInformatieobjectDto(
+                request.Bronorganisatie,
+                request.Creatiedatum.ToString("yyyy-MM-dd"),
+                request.Titel,
+                request.Auteur,
+                request.Taal,
+                request.Informatieobjecttype.ToString(),
+                Convert.ToBase64String(request.Inhoud),
+                request.Bestandsnaam,
+                request.Inhoud.Length,
+                request.Vertrouwelijkheidaanduiding,
+                request.Formaat,
+                "definitief",
+                // No usage-rights restrictions apply. Left null, OpenZaak rejects closing the related
+                // zaak with "indicatiegebruiksrecht-unset"; false records the deliberate "none" answer.
+                false),
+            "Creating the informatieobject", ct);
+
+        // 2. Relate it to the zaak (Zaken API — no CRS).
+        await PostAsync("/zaken/api/v1/zaakinformatieobjecten",
+            new ZaakInformatieobjectDto(request.Zaak.ToString(), created.ToString()),
+            "Relating the informatieobject to the zaak", ct);
+
+        return created;
+    }
+
     // POSTs a non-geo ZGW resource (resultaat/status — no CRS headers). Buffers the body so uwsgi gets
     // a Content-Length instead of a chunked body (as with zaak-create).
     private async Task PostAsync(string path, object dto, string action, CancellationToken ct)
@@ -96,6 +129,26 @@ public sealed class OpenZaakGateway(HttpClient http, OpenZaakOptions options) :
         await EnsureSuccessAsync(response, action, ct);
     }
 
+    // POSTs a non-geo ZGW resource and returns the created resource's URL (as PostAsync, but reads back
+    // the `url` of the created object). Buffers the body so uwsgi gets a Content-Length.
+    private async Task<Uri> PostForUrlAsync(string path, object dto, string action, CancellationToken ct)
+    {
+        using var message = new HttpRequestMessage(HttpMethod.Post, new Uri(options.BaseUrl, path))
+        {
+            Content = JsonContent.Create(dto),
+        };
+        message.Headers.Authorization =
+            new AuthenticationHeaderValue("Bearer", ZgwToken.Mint(options.ClientId, options.Secret));
+        await message.Content.LoadIntoBufferAsync(ct);
+
+        using var response = await http.SendAsync(message, ct);
+        await EnsureSuccessAsync(response, action, ct);
+
+        var created = await response.Content.ReadFromJsonAsync<CreatedDto>(ct)
+            ?? throw new InvalidOperationException($"OpenZaak returned an empty response for {action}");
+        return new Uri(created.Url);
+    }
+
     // EnsureSuccessStatusCode discards the response body; ZGW returns a JSON problem detail on 400 that
     // is essential for diagnosing a rejected request, so surface it in the exception.
     private static async Task EnsureSuccessAsync(HttpResponseMessage response, string action, CancellationToken ct)
@@ -182,4 +235,26 @@ public sealed class OpenZaakGateway(HttpClient http, OpenZaakOptions options) :
 
     private sealed record ResultaattypeDto(
         [property: JsonPropertyName("url")] string Url);
+
+    private sealed record CreatedDto(
+        [property: JsonPropertyName("url")] string Url);
+
+    private sealed record EnkelvoudigInformatieobjectDto(
+        [property: JsonPropertyName("bronorganisatie")] string Bronorganisatie,
+        [property: JsonPropertyName("creatiedatum")] string Creatiedatum,
+        [property: JsonPropertyName("titel")] string Titel,
+        [property: JsonPropertyName("auteur")] string Auteur,
+        [property: JsonPropertyName("taal")] string Taal,
+        [property: JsonPropertyName("informatieobjecttype")] string Informatieobjecttype,
+        [property: JsonPropertyName("inhoud")] string Inhoud,
+        [property: JsonPropertyName("bestandsnaam")] string Bestandsnaam,
+        [property: JsonPropertyName("bestandsomvang")] int Bestandsomvang,
+        [property: JsonPropertyName("vertrouwelijkheidaanduiding")] string Vertrouwelijkheidaanduiding,
+        [property: JsonPropertyName("formaat")] string Formaat,
+        [property: JsonPropertyName("status")] string Status,
+        [property: JsonPropertyName("indicatieGebruiksrecht")] bool IndicatieGebruiksrecht);
+
+    private sealed record ZaakInformatieobjectDto(
+        [property: JsonPropertyName("zaak")] string Zaak,
+        [property: JsonPropertyName("informatieobject")] string Informatieobject);
 }