Exercise templates

Exercises are reusable client components under app/src/screens/exercises/, referenced by lesson modules generated through the content pipeline. Each exercise type (for example: multiple choice, ordering, free response) is a template — the content pipeline fills it with generated data, it doesn't generate new exercise UI.

When you need a new interaction type, add the template once in app/, wire it into the client-side content map (catalog-map.ts), and it becomes available to every future course the pipeline generates — including courses you haven't written yet.