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/playwright.config.ts

@@ -0,0 +1,16 @@
+import { defineConfig, devices } from '@playwright/test';
+
+// The e2e runs inside the compose network (infra/run-e2e-check.sh); baseURL defaults to the
+// self-service service. Keep timeouts generous — the first navigation triggers the DigiD flow.
+export default defineConfig({
+  testDir: '.',
+  timeout: 90_000,
+  expect: { timeout: 15_000 },
+  retries: 1,
+  reporter: [['list']],
+  use: {
+    baseURL: process.env.SELF_SERVICE_URL ?? 'http://self-service',
+    trace: 'on-first-retry',
+  },
+  projects: [{ name: 'chromium', use: { ...devices['Desktop Chrome'] } }],
+});