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

TechHelper.Server/Services/Question/IQuestionService.cs

@@ -0,0 +1,11 @@
+using Entities.Contracts;
+using Entities.DTO;
+
+namespace TechHelper.Services.Beta
+{
+	public interface IQuestionService : IBaseService<QuestionDto, Guid>
+	{
+		Task<ApiResponse> FindByTitle(string title);
+		Task<ApiResponse> CheckTitlesExistence(IEnumerable<string> titles);
+	}
+}