List/home endpoints picked the family representative row via goods[0],
which drifted with the list sort parameter (cheapest under PRICE_ASC,
lowest id under DEFAULT ties), causing goodName and other
representative-derived fields to differ from the detail endpoint.
Extract pickFamilyRepresentative (goodPriority desc -> createdAt desc
-> id asc, same as getGoodByFamilyId) and use it in getGoods and
getHomeGoods grouping. Group ordering and API contracts unchanged.
