test(workflow): beoordeling escalation reassigns to teamlead (S-14, refs #15)

Failing Workflow Client tests for the 14-day escalation capability (ADR
proposal #98): acquire BeoordelingEscaleren external-worker jobs, reassign the
still-open Beoordelen task's candidate group behandelaar -> teamlead, and
complete the escalation job. Methods are stubbed to throw so the suite compiles
and fails on the new behaviour only.

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

services/domain/Big.Application/Ports.cs

@@ -86,3 +86,10 @@ public interface IRegistrationStore
 /// it) and the registration id it carries as a process variable.
 /// </summary>
 public sealed record OpenZaakJob(string JobId, RegistrationId RegistrationId);
+
+/// <summary>
+/// An acquired <c>BeoordelingEscaleren</c> escalation job (S-14): the Flowable job id and the process
+/// instance whose still-open <c>Beoordelen</c> task must be reassigned from behandelaar to teamlead
+/// once the 14-day boundary timer fires (ADR-0015).
+/// </summary>
+public sealed record EscalatieJob(string JobId, string ProcessInstanceId);