Batch list-membership lookup. For each apex, returns the lists (belonging to the caller) it appears in along with the per-item values (user-edited custom-column cells). A sidecar lists map carries the active column definitions for every list referenced, so callers can render label: value pairs without a follow-up fetch. Used to render list memberships on /search tiles + firm detail pages. Pass apex once for a single firm, or multiple times for a batch (max 200).