feat: 优化存档管理，增强链状态获取逻辑，添加 ISaveable 接口支持

Assets/_Game/Scripts/Core/Save/GameSaveManager.cs

@@ -195,7 +195,12 @@ namespace BaseGames.Core.Save
         public void SetChainCompleted(string chainId)
         { _current ??= new SaveData(); _current.EventChains.ChainStates[chainId] = "Completed"; }
         public IEnumerable<string> GetCompletedChains()
-            => _current?.EventChains.ChainStates.Keys ?? Enumerable.Empty<string>();
+        {
+            if (_current?.EventChains?.ChainStates == null) return System.Linq.Enumerable.Empty<string>();
+            return _current.EventChains.ChainStates
+                .Where(kv => kv.Value == "Completed")
+                .Select(kv => kv.Key);
+        }
 
         public bool IsFirstClear(string challengeId)
         {