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

TechHelper.Client/Pages/Exam/ExamEdit.razor

@@ -2,7 +2,6 @@
 @using Entities.DTO
 @using TechHelper.Client.Pages.Exam.ExamView
 @using TechHelper.Client.Services
-@using Entities.DTO
 @using TechHelper.Client.Exam
 
 <ExamView ParsedExam="@ExamDto"/>
@@ -20,7 +19,7 @@
 	[Inject]
 	private ISnackbar Snackbar { get; set; }
 
-	private AssignmentDto ExamDto { get; set; }
+	private ExamDto ExamDto { get; set; }
 
 	protected override async Task OnInitializedAsync()
 	{
@@ -31,7 +30,7 @@
 			try
 			{
 				var result = await ExamService.GetExam(parsedExamId);
-				if (result.Status) ExamDto = result.Result as AssignmentDto ?? new AssignmentDto();
+				if (result.Status) ExamDto = result.Result as ExamDto ?? new ExamDto();
 			}
 			catch (Exception ex)
 			{