Edit a fiber chain-of-custody model

Replaces a model's materials and/or facilityProcessIds — at least one is required, a key left out keeps its stored set, and a key sent may not be empty, so a set cannot be cleared (legacy silently ignored an empty facilityProcessIds). Duplicates keep their first entry. On a non-segregated model every sent material is stored as required and every other material in the catalogue as optional, whatever isRequired says; legacy answered 500 there when materials was left out. A material id the catalogue does not have answers 400 invalid_material_id (legacy stored it); facility-process ids are stored as sent. Responds with the model as the list shows it, in the { data, metadata } envelope (legacy answered the bare record). 404 not_found for an unknown id.