feat(子弹系统): 重构伤害计算并添加音效

将子弹的伤害属性从`damage`重命名为`baseDamage`，并引入`damageMultipliers`数组支持多段伤害
为火山武器添加三段攻击音效并调整伤害倍率
更新相关武器和子弹脚本以适配新的伤害系统

scripts/Contents/Bullets/Arrow.gd

@@ -18,7 +18,7 @@ func ai():
 		trail.emitting = true
 		hitbox.disabled = false
 	speed = (1 - lifeDistancePercent()) * initialSpeed
-	damage = speed * atk
+	baseDamage = speed * atk
 	PresetBulletAI.forward(self, rotation)
 	if speed < 1:
 		tryDestroy()