fix: 登录 UserInfo 构建改为串行查询，避免 DbContext 并发异常

Co-authored-by: Cursor <cursoragent@cursor.com>

src/SimpleAdmin.Api/Auth/AuthService.cs

@@ -460,13 +460,9 @@ public partial class AuthService(
             return cached;
         }
 
-        // 用户资料与权限并行，避免串行打两次慢查询
-        var userTask = userService.GetAsync(userId, cancellationToken);
-        var permissionsTask = userService.GetUserPermissionsAsync(userId, cancellationToken);
-        await Task.WhenAll(userTask, permissionsTask);
-
-        var userInfo = await userTask;
-        var permissions = await permissionsTask;
+        // 同一 scoped DbContext 不能并行查询，必须串行
+        var userInfo = await userService.GetAsync(userId, cancellationToken);
+        var permissions = await userService.GetUserPermissionsAsync(userId, cancellationToken);
         var menus = await BuildMenusByPermissionsAsync(permissions, cancellationToken);
 
         var dto = new UserInfoDto