docs(architecture): ADR-0011 approval status flow + demo note (refs #75)

Records the two non-obvious decisions: the ACL resolves the zaaktype eindstatus
(domain stays ZGW-ignorant), and the event-subscriber projects INGESCHREVEN from
the notification alone (hoofdObject + any status-create), never reading OpenZaak.

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

docs/demo-script.md

@@ -195,5 +195,35 @@ curl -fsS http://localhost:8140/openbaar/register | jq   # same public-safe view
 # → [ { "id": "<zaak-uuid>", "status": "INGEDIEND" } ]
 ```
 
-> The register shows `INGEDIEND` entries today; the approval transition to a terminal status
-> (e.g. `INGESCHREVEN`) lands with the approval flow (S-09b, #75).
+> The register shows `INGEDIEND` on submit; approval flips it to `INGESCHREVEN` — see S-09b below.
+
+---
+
+## S-09b — Approval flow (public visibility flips to INGESCHREVEN)
+
+**Outcome:** a behandelaar approves a submitted registration via a temporary admin endpoint (no
+behandel-portal yet — S-12). The approval sets the zaak's final status through the ACL, which flows
+back to the projection over NRC, and the openbaar register then shows the entry as `INGESCHREVEN`.
+
+**The path:** `POST /registrations/{id}/approve` (domain) → ACL sets the zaak eindstatus (ZGW
+`/statussen`) → OpenZaak → NRC → Event Subscriber projects `INGESCHREVEN` → openbaar register.
+
+```bash
+# 1. Full stack up, then drive submit → public INGEDIEND → approve → public INGESCHREVEN:
+make up
+make verify-e2e
+
+# 2. Or by hand: submit (as in S-09), note the reference, then approve it.
+#    The zaak is opened off the request path, so approve once GET shows a zaakUrl.
+ref="<registration-reference-from-the-confirmation>"
+curl -fsS http://localhost:8130/registrations/$ref | jq       # domain (host port 8130): wait for .zaakUrl
+curl -fsS -X POST http://localhost:8130/registrations/$ref/approve -i   # → 204 No Content
+
+# 3. The public register now shows the entry as approved.
+curl -fsS http://localhost:8140/openbaar/register | jq
+# → [ { "id": "<zaak-uuid>", "status": "INGESCHREVEN" } ]
+```
+
+> **End of walking skeleton** (S-09 + S-09b): submit → process → projection → public visibility, from
+> INGEDIEND through approval to INGESCHREVEN. The subscriber takes any post-creation status-set as the
+> approval (ADR-0011) — a walking-skeleton assumption that tightens when more transitions arrive (S-12+).