fix: 修复数据库与SignalR无法连接的问题

server/src/Controllers/ExamController.cs

@@ -15,19 +15,9 @@ public class ExamController : ControllerBase
 {
     private static NLog.Logger logger = NLog.LogManager.GetCurrentClassLogger();
 
-    private readonly ExamManager _examManager;
-    private readonly ResourceManager _resourceManager;
-    private readonly UserManager _userManager;
-
-    public ExamController(
-        ExamManager examManager,
-        ResourceManager resourceManager,
-        UserManager userManager)
-    {
-        _examManager = examManager;
-        _resourceManager = resourceManager;
-        _userManager = userManager;
-    }
+    private readonly ExamManager _examManager = new();
+    private readonly ResourceManager _resourceManager = new();
+    private readonly UserManager _userManager = new();
 
     /// <summary>
     /// 获取所有实验列表