Kits are ownership-backed club items: the owned instance stays in the
generic owned_cards inventory and only the two active roles get their own
table. This mirrors the squad_managers precedent and keeps every
FIFA-specific resourceId/wire concern in the game adapter.
* migration 0024: club_kit_assignments(club_id, slot, owned_card_id) with a
UNIQUE owned_card_id (one instance cannot hold both roles) and
ON DELETE CASCADE from owned_cards so a quick-sell clears the role.
* a BEFORE UPDATE OF club_id trigger clears the designation on a market
transfer, which moves ownership by UPDATE and so is not covered by the
cascade.
* set_active_club_kits replaces BOTH slots in one transaction, rejects
home == away, and validates each instance against current club ownership,
so a half-applied or dangling designation is not representable.
* get_active_club_kits revalidates ownership on read, so a stale row can
never surface another club's item.
* GET/PUT /club/kits expose the pair.
Tests cover restart persistence, replace/clear without duplicates, atomic
rejection of invalid references, and clearing via delete and transfer.
funman300