docs(workflow): ADR-0015 + demo note for beoordeling escalation (S-14, refs #15)

Record the escalation-via-external-worker decision (ADR-0015, from proposal #98)
and add the S-14 demo walkthrough that fires the 14-day timer early via Flowable's
management API to observe the reassignment to teamlead.

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

docs/demo-script.md

@@ -298,3 +298,48 @@ interrupting boundary event ends it → the werkbak drops the case.
 > DigiD submit → trek aanvraag in → ingetrokken is the Playwright happy path
 > (`tests/e2e/withdrawal.spec.ts`); the owner-scoping + workflow cancellation are covered by the
 > `Een registratie intrekken` acceptance scenarios and the domain live check.
+
+## S-14 — Beoordeling escalation: 14 days unclaimed → teamlead (#15, ADR-0015)
+
+A beoordeling a behandelaar does not pick up within 14 days escalates to the teamlead. A
+non-interrupting boundary timer on the `Beoordelen` task fires a `BeoordelingEscaleren` external task;
+the domain's escalation worker reassigns the still-open task's candidate group from `behandelaar` to
+`teamlead`, so it moves from the behandelaar werkbak into the teamlead's. The `Beoordelen` task keeps
+its identity throughout — only who may claim it changes.
+
+The timer is 14 days, so the demo fires it early through Flowable's management API (exactly what the
+verify-domain check automates):
+
+```bash
+# 1. Submit at the self-service portal (http://localhost:8140/, jan-burger / test123). The case
+#    parks at Beoordelen, visible in the behandelaar werkbak (http://localhost:8142/, merel-behandelaar)
+#    but NOT claimed.
+#
+# 2. Find the parked instance and its Beoordelen task, then fire the boundary timer early:
+FL=http://localhost:8090/flowable-rest/service
+PID=$(curl -s -u rest-admin:test -X POST "$FL/query/tasks" -H 'Content-Type: application/json' \
+  -d '{"processDefinitionKey":"registratie","taskDefinitionKey":"Beoordelen"}' \
+  | python3 -c 'import sys,json;print(json.load(sys.stdin)["data"][0]["processInstanceId"])')
+TID=$(curl -s -u rest-admin:test -X POST "$FL/query/tasks" -H 'Content-Type: application/json' \
+  -d '{"processDefinitionKey":"registratie","taskDefinitionKey":"Beoordelen"}' \
+  | python3 -c 'import sys,json;print(json.load(sys.stdin)["data"][0]["id"])')
+TJ=$(curl -s -u rest-admin:test "$FL/management/timer-jobs?processInstanceId=$PID" \
+  | python3 -c 'import sys,json;print(json.load(sys.stdin)["data"][0]["id"])')
+curl -s -u rest-admin:test -X POST "$FL/management/timer-jobs/$TJ" \
+  -H 'Content-Type: application/json' -d '{"action":"move"}'
+AJ=$(curl -s -u rest-admin:test "$FL/management/jobs?processInstanceId=$PID" \
+  | python3 -c 'import sys,json;print(json.load(sys.stdin)["data"][0]["id"])')
+curl -s -u rest-admin:test -X POST "$FL/management/jobs/$AJ" \
+  -H 'Content-Type: application/json' -d '{"action":"execute"}'
+#
+# 3. Within a couple of poll cycles the task's candidate group flips to teamlead:
+curl -s -u rest-admin:test "$FL/runtime/tasks/$TID/identitylinks"   # → [{"group":"teamlead","type":"candidate"}]
+```
+
+**The path:** BPMN non-interrupting `P14D` boundary timer on `Beoordelen` → `BeoordelingEscaleren`
+external task → domain escalation worker (`BeoordelingEscalatiePump`) → Workflow Client swaps the task's
+candidate group behandelaar → teamlead (§8.2).
+
+> Both branches (escalate after 14 days; no-op when completed in time) are covered by the
+> `Een beoordeling escaleren` acceptance scenarios and the Workflow Client unit tests; the timer firing
+> and reassignment are asserted live by the verify-domain check.