feat: entity definitions — player classes, monsters, items

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

entity/item.go

@@ -0,0 +1,36 @@
+package entity
+
+type ItemType int
+
+const (
+	ItemWeapon ItemType = iota
+	ItemArmor
+	ItemConsumable
+)
+
+type Item struct {
+	Name  string
+	Type  ItemType
+	Bonus int
+	Price int
+}
+
+type RelicEffect int
+
+const (
+	RelicHealOnKill RelicEffect = iota
+	RelicATKBoost
+	RelicDEFBoost
+	RelicGoldBoost
+)
+
+type Relic struct {
+	Name   string
+	Effect RelicEffect
+	Value  int
+	Price  int
+}
+
+func NewHPPotion() Item {
+	return Item{Name: "HP Potion", Type: ItemConsumable, Bonus: 30, Price: 20}
+}