重构项目结构，移除Assignment相关功能，优化Submission模块

TechHelper.Client/Pages/Exam/ExamManager.razor

@@ -4,7 +4,6 @@
 @using TechHelper.Client.Pages.Common.Exam
 
 @page "/exam/manage"
-@using Entities.DTO
 @using TechHelper.Client.Services
 @attribute [Authorize]
 
@@ -34,7 +33,7 @@ else
 	[CascadingParameter]
 	private Task<AuthenticationState> authenticationStateTask { get; set; }
 
-	private List<AssignmentDto> examDtos = new List<AssignmentDto>();
+	private List<ExamDto> examDtos = new List<ExamDto>();
 
 	private bool isloding = true;
 
@@ -51,7 +50,7 @@ else
 		var result = await ExamService.GetAllExam();
 		if (result.Status)
 		{
-			examDtos = result.Result as List<AssignmentDto> ?? new List<AssignmentDto>();
+			examDtos = result.Result as List<ExamDto> ?? new List<ExamDto>();
 			Snackbar.Add("加载成功", Severity.Info);
 		}
 		else