Shops and Currency

Money earned from battles, spent at a shop NPC on potions and balls.

Why deferred: Items barely matter yet (two items, and potions are free in the starting inventory), so an economy has nothing to price. The NPC effect system can host a shop interaction later; the save gains a money field then.

Revisit when: the item catalog grows (more ball tiers / battle items) — an economy is only as interesting as the things it sells.