feat(combat): 弹反投射物伤害目标层改为显式配置

ProjectileConfigSO 新增 ReflectedTargetLayers：弹反后写入 HitBox.TargetLayers 的目标层显式配置；留空(Nothing)有明确缺省语义=自动翻转（PlayerHurtBox 位换 EnemyHurtBox 位、其余位保留）。Projectile/ParryableProjectile 两条弹反路径统一走 ApplyReflectedTargetLayers。现有 6 个投射物配置资产已显式配为 EnemyHurtBox。

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

Assets/_Game/Scripts/Combat/ProjectileConfigSO.cs

@@ -26,5 +26,8 @@ namespace BaseGames.Combat
         [Header("弹反")]
         public float ParrySpeedMultiplier  = 1.2f;
         public float ParryDamageMultiplier = 2.0f;
+        [Tooltip("弹反后本投射物可造成伤害判定的 Layer（显式配置，写入 HitBox.TargetLayers）。" +
+                 "留空(Nothing) = 自动翻转：在原目标层基础上 PlayerHurtBox 位换为 EnemyHurtBox 位、其余位保留。")]
+        public LayerMask ReflectedTargetLayers;
     }
 }