feat(战斗系统): 重构子弹追踪逻辑，使用实体当前焦点位置替代鼠标位置

修改所有子弹追踪逻辑，统一使用launcher.currentFocusedPosition作为目标位置
在EntityBase中新增currentFocusedPosition字段，用于存储当前焦点位置
调整MTY角色的攻击距离参数，使用常量定义最小招架和攻击距离

scripts/Contents/Bullets/Arrow.gd

@@ -12,15 +12,15 @@ func register():
 	hitbox.disabled = true
 func ai():
 	if timeLived() < waitTime:
-		PresetBulletAI.lockLauncher(self, launcher, true)
-		rotation = position.angle_to_point(get_global_mouse_position()) + offsetRotation
+		PresetBulletAI.lockLauncher(self , launcher, true)
+		rotation = position.angle_to_point(launcher.currentFocusedPosition) + offsetRotation
 		return
 	else:
 		trail.emitting = true
 		hitbox.disabled = false
 	speed = (1 - lifeTimePercent()) * initialSpeed
 	baseDamage = speed * atk
-	PresetBulletAI.forward(self, rotation)
+	PresetBulletAI.forward(self , rotation)
 	if speed < 1:
 		tryDestroy()
 func succeedToHit(_dmg: float, _entity: EntityBase):