Find other files in the space that share entities with this one

Returns { files } — documents in the same space connected to :fileId through shared entities, ranked by score (more or rarer shared entities score higher). Each item has fileId, score, and shared (the overlapping entities as { entityId, name, type }). Use it for ‘documents related to this one’. Requires space:read on :spaceId; missing access surfaces as a 404.