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

TechHelper.Client/Pages/Common/QuestionCardDialog.razor

@@ -9,7 +9,7 @@
         </MudText>
     </TitleContent>
     <DialogContent>
-        <TechHelper.Client.Pages.Exam.AssignmentQuestionEdit AssignmentQuestion="Questions"/>
+        <TechHelper.Client.Pages.Exam.ExamQuestionEdit ExamQuestion="Questions"/>
     </DialogContent>
     <DialogActions>
         <MudButton OnClick="Cancel">Cancel</MudButton>
@@ -22,7 +22,7 @@
     private IMudDialogInstance MudDialog { get; set; }
 
     [Parameter]
-    public AssignmentQuestionDto Questions { get; set; } = new AssignmentQuestionDto();
+    public ExamQuestionDto Questions { get; set; } = new ExamQuestionDto();
 
     private void Cancel() => MudDialog.Cancel();