feat(战斗系统): 改进敌人生成逻辑以围绕玩家位置生成

修改Wave.spawn方法以接受中心点参数，使敌人生成位置围绕玩家
在Starter和MakeFeed面板中调用spawnWave时计算玩家中心位置
重构EntityBase添加getPlayers方法获取所有玩家实体
重命名WorldManager.nextWave为doNextWave以更清晰表达意图

scripts/Statemachine/EntityBase.gd

@@ -466,7 +466,7 @@ func kill():
 	pass
 
 static func findPlayer(playerName: String) -> EntityBase:
-	for i in WorldManager.tree.get_nodes_in_group("players"):
+	for i in getPlayers():
 		if i.displayName == playerName:
 			return i
 	return null
@@ -493,5 +493,15 @@ static func generate(
 	if addToWorld:
 		WorldManager.rootNode.spawn(instance)
 	return instance
-static func getMobs():
-	return WorldManager.tree.get_nodes_in_group("mobs")
+static func getMobs() -> Array[EntityBase]:
+	var result: Array[EntityBase] = []
+	for entity in WorldManager.tree.get_nodes_in_group("mobs"):
+		if entity:
+			result.append(entity)
+	return result
+static func getPlayers() -> Array[EntityBase]:
+	var result: Array[EntityBase] = []
+	for entity in WorldManager.tree.get_nodes_in_group("players"):
+		if entity:
+			result.append(entity)
+	return result