feat(workflow): beoordeling escalation to teamlead after 14 days (S-14, closes #15) (#99)

## What & why

S-14: a beoordeling a behandelaar does not pick up within **14 days** escalates to the **teamlead**.

A non-interrupting `P14D` boundary timer on the `Beoordelen` user task fires an external-worker task
(`BeoordelingEscaleren`); the domain's escalation worker reassigns the still-open task's candidate group
from `behandelaar` to `teamlead`. The task keeps its identity — only who may claim it changes. The
escalation-via-external-worker decision is recorded in **ADR-0015** (proposal #98); it upholds §8.2
(the Workflow Client stays the only code that talks to Flowable) and keeps Flowable a stock image.

Closes #15

## Definition of Done

- [x] Linked Gitea issue (above).
- [x] Failing test committed before the implementation.
- [x] Implementation makes the test pass; refactor commit if structure improved.
- [x] Conventional Commits referencing the issue (`refs #NN`).
- [x] CI green — all Gitea Actions jobs.
- [x] `docker compose up` from a fresh clone reaches green health checks within 3 minutes (no new services; escalation is additive to the domain worker).
- [x] Docs updated (ADR-0015, demo note).
- [x] ADR added (`docs/architecture/adr-0015-beoordeling-escalation.md`).
- [x] Demo note in `docs/demo-script.md`.

## How it was built (TDD)

- **Workflow Client** (`IBeoordelingEscalatieClient`): acquire `BeoordelingEscaleren` jobs → find the open `Beoordelen` task in the instance → add `teamlead`/remove `behandelaar` candidate group → complete the job. Red → green.
- **Escalation drain loop** (`BeoordelingEscalatieProcessor`) + hosted `BeoordelingEscalatiePump`, mirroring the OpenZaak worker. Red → green.
- **BPMN**: non-interrupting `P14D` boundary timer on `Beoordelen` → external task → escalation end.
- **Both branches** (escalate after timeout; no-op when completed in time) covered by the `Een beoordeling escaleren` acceptance scenarios + Workflow Client unit tests.
- **Live integration**: `verify-domain` fires the timer early via Flowable's management API and asserts the reassignment to teamlead.

## Notes for reviewers

- Interface segregation: escalation is on `IBeoordelingEscalatieClient`, separate from the OpenZaak worker's `IExternalWorkerClient`.
- Reassignment is two REST hops (add teamlead, remove behandelaar); idempotent on redelivery — see ADR-0015 consequences.
- Local checks green: domain unit tests (104), acceptance (13), `dotnet format --verify-no-changes`, Release build (0 errors), **domain mutation 96.69%** (break 90). The `run-domain-check.sh` escalation path is CI-verified on verify-stack (local full-stack run is constrained here).
- `BeoordelingEscalatiePump` excluded from mutation, mirroring the existing `OpenZaakJobPump` exclusion.

Reviewed-on: #99

tests/acceptance/Steps/EenBeoordelingEscalerenSteps.cs

@@ -0,0 +1,44 @@
+using Acceptance.Support;
+using Big.Infrastructure;
+using Microsoft.Extensions.Logging.Abstractions;
+using Reqnroll;
+using Xunit;
+
+namespace Acceptance.Steps;
+
+/// <summary>Bindings for <c>EenBeoordelingEscaleren.feature</c> (S-14). Drives the escalation worker
+/// (<see cref="BeoordelingEscalatieProcessor"/>) against an in-memory Flowable stand-in; one instance
+/// per scenario. Escalation has no domain-aggregate surface — it only reassigns who may claim the
+/// still-open Beoordelen task — so the scenario asserts on the task's candidate group.</summary>
+[Binding]
+[Scope(Feature = "Een beoordeling escaleren")]
+public sealed class EenBeoordelingEscalerenSteps
+{
+    private readonly InMemoryEscalatieClient _flowable = new();
+    private string _processInstanceId = "";
+
+    [Given("a registration parked at the Beoordelen task for the behandelaar")]
+    public void GivenARegistrationParkedForTheBehandelaar()
+        => _processInstanceId = _flowable.ParkBeoordeling();
+
+    [When("the 14-day escalation timer fires")]
+    public void WhenTheEscalationTimerFires()
+        => _flowable.FireEscalationTimer(_processInstanceId);
+
+    [When("the behandelaar completes the beoordeling before the timer fires")]
+    public void WhenTheBehandelaarCompletesBeforeTheTimer()
+        => _flowable.CompleteBeoordeling(_processInstanceId);
+
+    [When("the escalation worker runs")]
+    public async Task WhenTheEscalationWorkerRuns()
+        => await new BeoordelingEscalatieProcessor(
+            _flowable, NullLogger<BeoordelingEscalatieProcessor>.Instance).PumpOnceAsync(5);
+
+    [Then("the beoordeling is reassigned to the teamlead")]
+    public void ThenTheBeoordelingIsReassignedToTheTeamlead()
+        => Assert.Equal("teamlead", _flowable.CandidateGroupFor(_processInstanceId));
+
+    [Then("the beoordeling stays with the behandelaar")]
+    public void ThenTheBeoordelingStaysWithTheBehandelaar()
+        => Assert.Equal("behandelaar", _flowable.CandidateGroupFor(_processInstanceId));
+}