- engine: step.frame executes fill/submit in the matching iframe's
  execution context (cross-origin auth widgets, e.g. Piano ID)
- engine: step.click {text} clicks a main-frame button by visible text
  (opens login modals); loggedOutSelector = logged-in when absent
- logins/nikkei-world.json: Piano two-step form (email -> password in
  auth.asia.nikkei.com iframe), validated with a real login