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

TechHelper.Client/Pages/Author/Registration.razor.cs

@@ -1,11 +1,11 @@
 using TechHelper.Client.HttpRepository;
-using Entities.DTO;
 using Microsoft.AspNetCore.Components;
 using MudBlazor;
 using System.Text.RegularExpressions;
 using TechHelper.Features;
 using Entities.Contracts;
 using TechHelper.Client.Services;
+using Entities.DTO;
 
 namespace TechHelper.Client.Pages.Author
 {