feat(#78): one citizen reference across self-service and the openbaar register (#79)

## What & why

Before this change the self-service confirmation and the openbaar register showed **different** identifiers, so a citizen could not look their registration back up (#78). Now both surface the same **reference**:

- **domain → ACL (write):** the domain `registrationId` is set as the zaak's `identificatie` on `POST /zaken`.
- **event-subscriber → ACL (read):** the subscriber reads the zaak's `identificatie` back through the ACL (§8.1 — only the ACL talks to ZGW) via a new `POST /zaken/reference`, and stores it on the projection row **and** the `processed_notifications` replay log.
- **BFF + openbaar:** the public view exposes `id/status/reference` (never bsn/naam) and searches by id or reference; the register's "Referentie" column shows the reference.

Storing the reference in the replay log keeps ADR-0008's **rebuild-is-log-only** invariant intact — `/admin/rebuild` reproduces the reference without re-reading the ACL.

Decision recorded in **ADR-0012**.

## Definition of Done

- [x] Linked issue: #78
- [x] Tests written first; red → green per layer
- [x] Unit + acceptance green (`make unit`): domain 49, acl 27, bff 20, event-subscriber 19, acceptance 7
- [x] Frontend lint + test green (`nx run-many -t lint test`)
- [x] Mutation ≥ break(90): acl 100%, event-subscriber 100%, bff 100%, domain 98.41% (pre-existing FlowableWorkflowClient baseline, untouched)
- [x] e2e extended: confirmation reference == register reference
- [x] openapi.json + api-client regenerated (drift guard green)
- [x] ADR-0012 added; demo-script note appended
- [x] `Acl__BaseUrl` wired for the subscriber in compose

closes #78

Reviewed-on: #79

tests/e2e/registration.spec.ts

@@ -26,15 +26,22 @@ test('DigiD login → submit → public INGEDIEND → approve → public INGESCH
 
   // The openbaar register (anonymous, its own origin) shows the submitted entry once the projection
   // catches up. The projection updates asynchronously (NRC → event-subscriber), and the register loads
-  // on open, so reload until a submitted (INGEDIEND) row appears.
+  // on open, so reload until *this* submission's row appears. We poll on the reference cell (not a
+  // generic INGEDIEND cell): the shared verify stack already holds INGEDIEND rows from earlier checks,
+  // so a status-only poll would short-circuit on a stale row before our row is projected.
   await page.goto('http://openbaar/');
   await expect(page.getByRole('heading', { name: /Openbaar BIG-register/i })).toBeVisible();
+
+  // #78: the reference shown in the public register must be the exact one the citizen saw on the
+  // submit confirmation — no mismatch between the two portals.
   await expect
     .poll(async () => {
       await page.reload();
-      return page.getByRole('cell', { name: 'INGEDIEND' }).count();
+      return page.getByRole('cell', { name: reference }).count();
     }, { timeout: 30_000, intervals: [1_000, 2_000, 3_000, 5_000] })
     .toBeGreaterThan(0);
+  await expect(page.getByRole('row', { name: reference }).getByRole('cell', { name: 'INGEDIEND' }))
+    .toBeVisible();
 
   // Approve via the temporary admin endpoint (reached directly on the compose network, as a
   // behandelaar would until the behandel-portal exists — S-12). The zaak is opened off the request
@@ -49,11 +56,12 @@ test('DigiD login → submit → public INGEDIEND → approve → public INGESCH
   const approve = await request.post(`http://domain:8080/registrations/${reference}/approve`);
   expect(approve.status()).toBe(204);
 
-  // The approval flows back to the projection; the openbaar register now shows it as INGESCHREVEN.
+  // The approval flows back to the projection; the openbaar register now shows *our* row (matched by
+  // its reference) as INGESCHREVEN.
   await expect
     .poll(async () => {
       await page.reload();
-      return page.getByRole('cell', { name: 'INGESCHREVEN' }).count();
+      return page.getByRole('row', { name: reference }).getByRole('cell', { name: 'INGESCHREVEN' }).count();
     }, { timeout: 30_000, intervals: [1_000, 2_000, 3_000, 5_000] })
     .toBeGreaterThan(0);
 });