feat(TimeCountDown): 实现倒计时功能

Assets/Script/Gameplay/Global/GameFlowManager.cs

@@ -0,0 +1,24 @@
+using System;
+using Core;
+using UnityEngine;
+
+namespace Script.Gameplay.Global
+{
+    public enum GameState
+    {
+        Boot,        // 初始化
+        MainMenu,    // 主菜单
+        Playing,     // 游戏中
+        Paused,      // 暂停
+        GameOver,    // 游戏结束
+        Victory      // 胜利
+    }
+    
+    public class GameFlowManager : MonoSingleton<GameFlowManager>
+    {
+        private void Start()
+        {
+            GameCountdownManager.Instance.StartLevelTimer();
+        }
+    }
+}