A material may be private: only its author and the users it is shared
with see it. Every student read (list, detail, course detail and
counters, the checklist linked material, the token twins) goes through
one visibility fragment. Existing materials stay public with no author.
GET/PUT /_bm/api/v1/materials/{id}/access let the author, a material
manager, toggle the flag and pick the users; the first change of an
author-less material makes the caller its author.
Dashboard, courses with counters, schedule, meetings, deadlines,
readings with per-user progress (mark and unmark) and paginated
published materials with tags and files, behind golem15.user's
jwt.auth. Responses are built field by field with Warsaw RFC 3339
timestamps; bad query parameters answer 422 in Laravel's shape.
