[Fixed] Forum file downloads now fully respect forum membership

We identified and closed a gap where the direct download, view, and play links for files attached to a forum did not re-check that forum's membership the way the forum's Files tab does. In a member-only or role-restricted forum, someone who was not a member could have reached one of those files through its direct link. Every file-serving path now enforces the same membership and role checks as the forum itself. Fixed and deployed to every site. No action is needed on your part.