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

BACKLOG.md

@@ -209,9 +209,13 @@ Split (issue #11 closed) into two independently-demoable slices per §13 — the
 
 #### S-10b · Real diploma upload stored via the ACL Documenten API — #103
 
-**Outcome:** the self-service "Documenten aanleveren" action becomes a real file upload; the document is stored in the ZGW Documenten (DRC) API and related to the zaak, with all document calls routed through the ACL (§8.1), and the zaak is set to a cancellation status on timeout expiry. Builds on the S-10a trigger/wait. Depends on #102.
+**Outcome:** the self-service "Documenten aanleveren" action becomes a real file upload; the file (base64-encoded end-to-end) is stored in the ZGW Documenten (DRC) API as an `enkelvoudiginformatieobject` and related to the zaak, with all document calls routed through the ACL (§8.1, ADR-0018). Builds on the S-10a trigger/wait. Depends on #102.
 
-**Acceptance:** ACL Documenten gateway integration test; Playwright e2e uploads a real document; the openbaar/zaak reflects the stored document.
+**Acceptance:** ACL Documenten gateway integration test (real OpenZaak); Playwright e2e uploads a real PDF.
+
+#### S-10c · Close the ZGW zaak on document-timeout expiry — #106
+
+**Outcome:** when the 30-day term lapses (S-10a `RegistratieVerlopen`), the ZGW zaak is set to a cancellation status (not just the domain aggregate → `Verlopen`). Adds a cancellation statustype/resultaattype to the seed + an ACL method + expiry-worker wiring. Carved from S-10b (ADR-0017/0018). Depends on #103.
 
 ### S-11 · Withdrawal (Flow 3)