Compose a document into a branded PDF

Renders the markdown through a style profile and files the PDF back onto the session as its own artifact, beside the markdown it came from. styleProfileId picks a Brand profile, configId a /v1 compose template; with neither, the org default profile is used, or the platform’s plain layout when the org has none. Authorization: the same gate as every session route — work_session:read (or comment to write) on the session, OR space:contribute on one of its linked spaces; a desk session only for its owner. Any denial is 404.