test(e2e): walking-skeleton Playwright happy path + verify-e2e lane (refs #68)

tests/e2e Playwright spec drives DigiD login (jan-burger/test123) → submit →
confirmation against the compose-served portal. run-e2e-check.sh runs it inside the
compose network (node container, browser installed at runtime) so the token issuer
(keycloak:8080) matches the BFF authority (ADR-0010). Wired as verify-e2e (Makefile +
verify chain + a verify-stack CI step).

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

tests/e2e/package.json

@@ -0,0 +1,8 @@
+{
+  "name": "e2e",
+  "private": true,
+  "description": "Playwright walking-skeleton e2e (S-08d) — run inside the compose network by infra/run-e2e-check.sh.",
+  "devDependencies": {
+    "@playwright/test": "1.61.1"
+  }
+}