feat(ChainGun): 为链式机枪添加子弹数量属性并调整子弹生成逻辑

修改链式机枪的武器脚本、场景配置和子弹脚本，新增count属性控制子弹数量
子弹生成时根据count值调整位置分布，同时更新UI描述文本

scripts/Contents/Bullets/ChainGun.gd

@@ -1,9 +1,14 @@
 extends BulletBase
 
+var count: int = 1
+
 @onready var anchor: Node2D = $"%anchor"
 
 func spawn():
-	for i in BulletBase.generate(ComponentManager.getBullet("PurpleCrystalSmall"), launcher, anchor.global_position, rotation):
-		i.damage = damage
+	for j in count:
+		for i in BulletBase.generate(ComponentManager.getBullet("PurpleCrystalSmall"), launcher, anchor.global_position, rotation):
+			i.damage = damage
+			var dir = Vector2.from_angle(i.rotation).rotated(deg_to_rad(-90))
+			i.global_position += dir * (count - j * 2) * 20 / 2
 func ai():
-	PresetBulletAI.lockLauncher(self, launcher, true)
+	PresetBulletAI.lockLauncher(self, launcher, true)