Add integration + Playwright smoke suite for post-deploy QA validation

Existing coverage was one integration test and zero e2e tests. Adds the thin,
high-value integration/e2e layer unit tests can't reach (real Postgres wire
contract, real browser flows) and wires it as a post-deploy smoke gate.

- Seed a deterministic dev/QA admin user and fixed Development env key so
  HTTP-only tests can authenticate without per-run registration.
- Expand the API integration suite: disabled-flag, unauthorized access,
  environment-document bootstrap, identity-override precedence, and auth
  login scenarios, reusing the existing black-box HTTP+Npgsql harness.
- Add a Playwright suite for the admin SPA: login, nav, project/environment
  context selection, and feature create/toggle, against the real API.
- Bind QA Postgres to 127.0.0.1 for direct seeding, add smoke-qa.sh and an
  ensure_node() bootstrap (the qa runner has no Node today), and wire a new
  smoke-qa CI job after deploy-qa.

.gitignore

@@ -438,6 +438,11 @@ dist-ssr/
 # TypeScript incremental build cache
 *.tsbuildinfo
 
+# Playwright
+src/admin/test-results/
+src/admin/playwright-report/
+src/admin/e2e/.auth/
+
 # Jest test coverage reports
 coverage/
 .nyc_output/