fix: 修复数据库与SignalR无法连接的问题

server/src/Controllers/DataController.cs

@@ -18,16 +18,11 @@ public class DataController : ControllerBase
 {
     private static NLog.Logger logger = NLog.LogManager.GetCurrentClassLogger();
 
-    private readonly Database.UserManager _userManager;
+    private readonly Database.UserManager _userManager = new();
 
     // 固定的实验板IP,端口,MAC地址
     private const string BOARD_IP = "169.254.109.0";
 
-    public DataController(Database.UserManager userManager)
-    {
-        _userManager = userManager;
-    }
-
     /// <summary>
     /// 获取本机IP地址（优先选择与实验板同网段的IP）
     /// </summary>