Return the trip_state_events audit trail for trip_id, ordered newest-first. Both trip-level events (segmentId null) and segment-level events are included unless segment_id is specified. Pagination uses an opaque keyset cursor over (occurredAt DESC, id DESC). 404 when the trip does not exist; 403 when the trip exists but belongs to a different user. Note: segment_id filters events to a single segment but does not validate that the segment belongs to the trip; non-matching segment UUIDs simply yield an empty list.