Get fan insights in bulk

Returns detailed insights for multiple fans in a single request.

This endpoint is optimized for chat list screens that need to hydrate fan insights without per-fan round trips.

Every field carries the same meaning as on GET /insights/fans/{userUuid}, including which money fields are net of reversals and which are gross, and the same absence of caching.

<Note>Maximum 20 fan UUIDs per request.</Note>