Party moves off a global singleton onto each save slot, letting
START_BATTLE pick specific active-order members to bring into a fight,
and round-trips through save/load via saveslotver1. A corrupt slot load
now flags the cache and shows a red "Corrupted Save" warning in the
select-save UI instead of silently resetting.
Co-Authored-By: Claude Sonnet 5 <[email protected]>
