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/Features/EenBeoordelingEscaleren.feature

@@ -0,0 +1,22 @@
+# language: en
+# Drives S-14 (#15). A beoordeling a behandelaar does not pick up within 14 days escalates to the
+# teamlead: a non-interrupting boundary timer parks a BeoordelingEscaleren job (ADR-0015) which the
+# escalation worker drains, reassigning the still-open Beoordelen task's candidate group to teamlead.
+# A beoordeling completed before the timer fires does not escalate. This scenario exercises the
+# escalation worker against an in-memory Flowable stand-in; the timer firing live is verify-domain.
+Feature: Een beoordeling escaleren
+  Als teamleider wil ik dat een beoordeling die na 14 dagen niet is opgepakt naar mij escaleert
+  zodat aanvragen niet blijven liggen.
+
+  Scenario: Na 14 dagen zonder oppakken escaleert de beoordeling naar de teamlead
+    Given a registration parked at the Beoordelen task for the behandelaar
+    When the 14-day escalation timer fires
+    And the escalation worker runs
+    Then the beoordeling is reassigned to the teamlead
+
+  Scenario: Een tijdig afgeronde beoordeling escaleert niet
+    Given a registration parked at the Beoordelen task for the behandelaar
+    When the behandelaar completes the beoordeling before the timer fires
+    And the 14-day escalation timer fires
+    And the escalation worker runs
+    Then the beoordeling stays with the behandelaar