feat(domain): RegistratieVerlopen worker + processor expire on document timeout (refs #102)

Adds RegistratieVerlopenJob, IRegistratieVerlopenClient, the ExpireRegistrationWorker
application handler, and the RegistratieVerlopenProcessor drain loop — the timeout
counterpart to the OpenZaak/escalation worker trios.

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

services/domain/Big.Application/ExpireRegistrationWorker.cs

@@ -0,0 +1,34 @@
+using Big.Domain;
+
+namespace Big.Application;
+
+/// <summary>
+/// Handles one acquired <c>RegistratieVerlopen</c> external-worker job (S-10a, ADR-0017): load the
+/// registration the job correlates to and expire it to VERLOPEN — the 30-day document-wait timer fired
+/// before the documents arrived, so the case is cancelled. Pure application logic over ports; it knows
+/// nothing of Flowable. The polling loop that feeds it jobs lives in Infrastructure. Mirrors
+/// <see cref="OpenZaakWorker"/>.
+/// </summary>
+public sealed class ExpireRegistrationWorker(IRegistrationStore store)
+{
+    /// <summary>
+    /// Process the job. Idempotent: a redelivered job whose registration is already VERLOPEN is a
+    /// no-op — not persisted again (§8.6, at-least-once delivery). An unknown registration is an error:
+    /// it throws, leaving the job un-completed for Flowable to redeliver.
+    /// </summary>
+    public async Task HandleAsync(RegistratieVerlopenJob job, CancellationToken ct = default)
+    {
+        ArgumentNullException.ThrowIfNull(job);
+
+        var registration = await store.GetAsync(job.RegistrationId, ct)
+            ?? throw new InvalidOperationException(
+                $"No registration {job.RegistrationId} for RegistratieVerlopen job {job.JobId}.");
+
+        // A redelivered job whose registration is already VERLOPEN completes without persisting again.
+        if (registration.Status == RegistrationStatus.Verlopen)
+            return;
+
+        registration.Expire();
+        await store.SaveAsync(registration, ct);
+    }
+}