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

TechHelper.Server/Services/School/ISchoolService.cs

@@ -0,0 +1,9 @@
+using Entities.DTO;
+
+namespace TechHelper.Services.Beta
+{
+    public interface ISchoolService : IBaseService<SchoolDto, Guid>
+    {
+        Task<ApiResponse> GetSchoolByNameAsync(string schoolName);
+    }
+}