wix/Detox ? reverse-engineered prompt

Build me a simple end to end testing setup for a React Native app using Detox.

I want to be able to run tests on both Android and iPhone simulators, write the tests in JavaScript, and have them interact with the app like a real person would, typing, tapping, and checking that screens show up correctly. Please include a small example test for a login flow, plus whatever setup is needed so it works smoothly in local development and in CI. Make the tests easy to debug, and keep the setup simple enough that I can copy it into an existing app.

If you need to, look up the current Detox docs online so the setup matches the latest recommendations. Also add clear instructions for how to run the tests and where to put new ones so I can extend it later.