Get Risks By Ids

Fetch several risks with the same joins and floors as GET /risks/{id}.

Batched over risk ids the way /files/metadata is over file ids, and for the same reason: the marketing analysis column mounts one card per finding and each card used to hit GET /risks/{id}, which is one pooled connection per card. Missing, other-company, and (for non-admins) rule-suppressed ids are left out of the mapping, so the caller maps back over the ids it asked for.