feat(角色): 为KukeMC添加重型紫水晶攻击技能

- 新增HeavyCrystal.gd脚本实现重型紫水晶子弹逻辑
- 在KukeMC角色中添加type=3的攻击类型
- 调整子弹场景配置，增加粒子特效和碰撞检测
- 移除旧的生成子角色和随机水晶攻击逻辑

scripts/Contents/Bullets/BossAttack/KukeMC/HeavyCrystal.gd

@@ -0,0 +1,17 @@
+extends BulletBase
+
+@onready var trail: GPUParticles2D = $"%trail"
+@onready var track: Node2D = $"%track"
+
+var readyTime: float = 1000
+
+func spawn():
+	trail.emitting = false
+func ai():
+	if timeLived() < readyTime:
+		rotation = launcher.position.angle_to_point(launcher.currentFocusedBoss.position)
+	else:
+		PresetBulletAI.forward(self, rotation)
+		speed += 1
+		trail.emitting = true
+		track.visible = false