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).

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Reviewed-on: #108

services/acl/Acl.Application/AclService.cs

@@ -37,4 +37,33 @@ public sealed class AclService(IZaakGateway gateway, AclDefaults defaults, ICloc
 
         return gateway.GetZaakIdentificatieAsync(zaakUrl, ct);
     }
+
+    /// <summary>
+    /// Store an uploaded diploma against the zaak (S-10b): default-fill the ZGW-mandatory document
+    /// fields (informatieobjecttype, bronorganisatie, vertrouwelijkheidaanduiding, taal, creatiedatum)
+    /// and hand the file to the gateway, which creates the informatieobject and relates it to the zaak.
+    /// The domain supplies only the zaak, the bytes, and the file's name/type (§8.1).
+    /// </summary>
+    public Task<Uri> StoreDiplomaAsync(Uri zaakUrl, byte[] content, string fileName, string contentType, CancellationToken ct = default)
+    {
+        ArgumentNullException.ThrowIfNull(zaakUrl);
+        ArgumentNullException.ThrowIfNull(content);
+        ArgumentException.ThrowIfNullOrWhiteSpace(fileName);
+        ArgumentException.ThrowIfNullOrWhiteSpace(contentType);
+
+        var request = new DocumentRequest(
+            defaults.Bronorganisatie,
+            defaults.InformatieobjecttypeUrl,
+            defaults.Vertrouwelijkheidaanduiding,
+            zaakUrl,
+            clock.Today,
+            Titel: "Diploma",
+            Auteur: "zorgprofessional",
+            Taal: "nld",
+            Bestandsnaam: fileName,
+            Formaat: contentType,
+            Inhoud: content);
+
+        return gateway.StoreDocumentAsync(request, ct);
+    }
 }