feat(workflow): document-wait task + 30-day timeout cancellation (S-10a, closes #102) (#105)

## What & why

S-10a, the **workflow/timeout spine** of the (split) document-upload slice: the registratie process
now parks at a **`WachtOpDocumenten`** user task with an **interrupting `P30D` boundary timer**. When
the documents arrive the task completes and the process continues into the diploma routing (S-13) →
Beoordelen; if the 30 days lapse, the timer cancels the wait, runs a `RegistratieVerlopen`
external-worker task, and the domain expires the aggregate to a new terminal status **`Verlopen`**.
Backend only — the real upload trigger (portal → BFF → ACL → Documenten API) is S-10b (#103).

Closes #102

Mechanism recorded in **ADR-0017**; opened as proposal #104. Mirrors the S-14 escalation
(boundary-timer + external-worker) and S-11 withdrawal (interrupting cancel) patterns.

## Definition of Done

- [x] Linked Gitea issue (above).
- [x] Failing test committed before the implementation (red→green pairs per layer).
- [x] Implementation makes the test pass.
- [x] Conventional Commits referencing the issue (`refs #102`).
- [ ] CI green — all Gitea Actions jobs (pending on this PR).
- [x] `docker compose up` health unaffected (no new services; deploy path unchanged).
- [x] Docs updated (ADR-0017, demo-script, BACKLOG split).
- [x] ADR added (`docs/architecture/adr-0017-document-wait-timeout-cancellation.md`).
- [x] Demo note in `docs/demo-script.md`.

## Notes for reviewers

- **Domain** (`Registration.Expire()` + `Verlopen`), **application** (`ExpireRegistrationWorker`),
  **infra** (`RegistratieVerlopenProcessor`/`Pump`, `IRegistratieVerlopenClient`, Flowable
  acquire/complete + `CompleteDocumentWaitAsync`) — the timeout counterpart to the OpenZaak/escalation
  worker trios; idempotent per §8.6.
- **BPMN** verified live against a `flowable-rest` probe: complete `WachtOpDocumenten` → routes to
  Beoordelen; fire the P30D timer → `RegistratieVerlopen` job (carrying `registrationId`) + the wait
  task cancelled. `verify-domain` exercises both branches in-stack (completes the wait in every existing
  block; fires the timer and asserts `Verlopen` in a new block).
- **Scope boundary:** on expiry the aggregate goes `Verlopen` and the process ends, but the ZGW *zaak*
  is not yet set to a cancellation status — that needs a new ACL method + statustype seeding and is
  folded into S-10b (noted in ADR-0017).
- `CompleteDocumentWaitAsync` is built and HTTP-tested here but not yet called from a domain endpoint;
  S-10b wires the upload trigger to it.

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

Reviewed-on: #105

services/domain/Big.Tests/RegistrationTests.cs

@@ -294,4 +294,63 @@ public class RegistrationTests
         Assert.Contains("only an INGEDIEND", ex.Message);
         Assert.Equal(RegistrationStatus.Afgewezen, registration.Status);
     }
+
+    [Fact]
+    public void Expiring_an_ingediend_registration_sets_it_verlopen()
+    {
+        // The 30-day document-wait timer fired before the documents arrived (S-10a): the case is
+        // cancelled and the aggregate becomes terminal VERLOPEN.
+        var registration = Registration.Submit("123456782");
+
+        registration.Expire();
+
+        Assert.Equal(RegistrationStatus.Verlopen, registration.Status);
+    }
+
+    [Fact]
+    public void Expiring_needs_no_zaak()
+    {
+        // The timer fires on a purely time-based boundary; expiry does not depend on the zaak.
+        var registration = Registration.Submit("123456782");
+
+        registration.Expire();
+
+        Assert.Equal(RegistrationStatus.Verlopen, registration.Status);
+        Assert.Null(registration.ZaakUrl);
+    }
+
+    [Fact]
+    public void Re_expiring_an_already_verlopen_registration_is_idempotent()
+    {
+        // The RegistratieVerlopen worker job may be redelivered (§8.6); re-expiring is a no-op.
+        var registration = Registration.Submit("123456782");
+        registration.Expire();
+
+        registration.Expire();
+
+        Assert.Equal(RegistrationStatus.Verlopen, registration.Status);
+    }
+
+    [Fact]
+    public void Expiring_an_approved_registration_is_rejected()
+    {
+        var registration = Registration.Submit("123456782");
+        registration.AttachZaak(new Uri("http://openzaak/zaken/api/v1/zaken/abc"));
+        registration.Approve();
+
+        var ex = Assert.Throws<InvalidOperationException>(() => registration.Expire());
+        Assert.Contains("only an INGEDIEND", ex.Message);
+        Assert.Equal(RegistrationStatus.Ingeschreven, registration.Status);
+    }
+
+    [Fact]
+    public void Expiring_a_withdrawn_registration_is_rejected()
+    {
+        var registration = Registration.Submit("123456782");
+        registration.Withdraw();
+
+        var ex = Assert.Throws<InvalidOperationException>(() => registration.Expire());
+        Assert.Contains("only an INGEDIEND", ex.Message);
+        Assert.Equal(RegistrationStatus.Ingetrokken, registration.Status);
+    }
 }