Generate client-side schema from Ecto.Schema changeset function.

As per diff attached and discussions in Krakow.

We're going from either a shape definition or an Ecto changeset to output a standard schema. Zod format is fine to start with.

This could be printed to stdout or written into the right location (like `./assets/src/db/schemas/:name.ts`) in the code structure generated by #48 .