Scaffold a feature screen

Every screen of an Expo Router app starts the same way: a script writes one feature folder (src/features/<feature>/) with a pure view, its model hook, a test for each, a thin route file and its route test, the message keys in every catalog, and, for a dynamic route, a valibot params parser with an invalid-link state; it registers the route and the screen in the app's contracts. A second script proves the feature is complete, on iOS and Android alike, before anything grows on it.

Rules that must hold