feat(角色): 添加熊boss的新攻击方式和音效

添加熊boss的四种攻击方式：
1. 箭雨攻击(ArrowSeven)
2. 太阳舞攻击(SunDance)
3. 永恒彩虹攻击(ForeverRainbow)
4. 冲刺攻击(BearSprint)

新增对应攻击音效资源
调整子弹追踪和伤害计算逻辑
添加冲刺粒子特效

scripts/Contents/Bullets/BossAttack/Bear/ForeverRainbow.gd

@@ -0,0 +1,20 @@
+extends BulletBase
+
+@export var allColor: GradientTexture1D = null
+
+var myColor: Color
+
+func register():
+	damage = 5
+	penerate = 1
+func spawn():
+	myColor = allColor.gradient.sample(randf())
+	setColor(myColor)
+
+func ai():
+	speed = (11000 - timeLived()) / 11000 * initialSpeed
+	rotation_degrees += speed / 10
+	PresetBulletAI.forward(self, rotation)
+
+func setColor(color: Color):
+	texture.modulate = color