```

feat(game): 删除弓箭手相关资源文件

删除了弓箭手预制体(Arrow.prefab)及其元文件，
同时移除了对应的白色箭矢材质(ArrowProjectile_White.mat)及元文件，
清理了项目中不再使用的箭矢相关资源。
```

Assets/Script/Projectile.cs

@@ -8,6 +8,7 @@ public class Projectile : MonoBehaviour
     private float speed;
     private float lifetime;
     private bool initialized;
+    private bool hasHit;
 
     public void Initialize(
         GameObject targetObject,
@@ -22,6 +23,7 @@ public class Projectile : MonoBehaviour
         speed = moveSpeed;
         lifetime = lifeTime;
         initialized = true;
+        hasHit = false;
 
         if (lifetime > 0f)
         {
@@ -42,7 +44,9 @@ public class Projectile : MonoBehaviour
             return;
         }
 
+        // 目标根节点位于脚底，只取水平差值，让箭保持当前高度平行飞行。
         Vector3 offset = target.transform.position - transform.position;
+        offset.y = 0f;
         if (offset.sqrMagnitude <= 0.01f)
         {
             HitTarget(target);
@@ -82,7 +86,7 @@ public class Projectile : MonoBehaviour
 
     private void TryHit(GameObject hitObject)
     {
-        if (!initialized || hitObject == null || IsOwner(hitObject))
+        if (!initialized || hitObject == null || target == null || IsOwner(hitObject))
         {
             return;
         }
@@ -95,12 +99,18 @@ public class Projectile : MonoBehaviour
 
     private void HitTarget(GameObject hitObject)
     {
+        if (hasHit)
+        {
+            return;
+        }
+
         WorldHealthBar healthBar = hitObject.GetComponentInParent<WorldHealthBar>();
         if (healthBar == null)
         {
             return;
         }
 
+        hasHit = true;
         healthBar.TakeDamage(damage);
         if (owner != null)
         {