refactor(enemy): 身体接触伤害改为常驻开启并与能力解耦

所有敌人默认常驻身体接触伤害:存活即开、死亡时经 PerformDeath 统一关碰撞体停止。
- ContactChaseAbility/AnimatedCeilingDropAbility 移除对 BodyContactDamage 的开关引用
- BodyContactDamage 语义改为常驻(更新注释)
- 脚手架 SetupHurtAndContactBoxes 去掉 contactEnabled 参数恒为 true,并把
  ContactDamageZone 的 HitBox._targetLayers 限定为 PlayerHurtBox(避免常驻后敌人互相误伤)
- 7 个敌人预制体:E001 启用 BodyContactDamage;E002/E004/E005/ChaoFeng 补齐
  ContactDamageZone(镜像 HurtBox 身体碰撞体);全部 _targetLayers 收敛为 PlayerHurtBox
- 更新 Docs/Guides/02 敌人搭建指南

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Assets/_Game/Prefabs/Enemies/E006/ENM_Huan.prefab

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