test(e2e): isolate the self-service specs with dedicated DigiD users (refs #111)

Resume-on-load (S-26) restores any open registration for the logged-in bsn, so on the
shared verify stack the specs can no longer share jan-burger: verify-domain submits as
jan-burger (123456782) before the e2e, and that open registration was being resumed on
login. Each self-service spec now uses its own citizen — registration→emma-burger,
resume→sanne-burger, withdrawal→lars-burger — none touched by the verify-* checks or
each other. jan-burger stays the documented citizen for the API-level verify checks.

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

tests/e2e/registration.spec.ts

@@ -13,8 +13,11 @@ test('DigiD submit → public INGEDIEND → documenten → behandelaar goedkeurt
   // Visiting the guarded page redirects to the Keycloak (mock DigiD) login.
   await page.goto('/');
 
-  // Keycloak's default login form (stable ids across themes).
-  await page.locator('#username').fill('jan-burger');
+  // Keycloak's default login form (stable ids across themes). Its own DigiD user: the verify-* API
+  // checks submit as jan-burger (bsn 123456782) before the e2e runs on the shared stack, and
+  // resume-on-load (S-26) would otherwise restore one of those on login — so each self-service spec
+  // uses a dedicated citizen no other actor touches.
+  await page.locator('#username').fill('emma-burger');
   await page.locator('#password').fill('test123');
   await page.locator('#kc-login').click();