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

Entities/DTO/Exam/ExamQuestionDto.cs

@@ -0,0 +1,33 @@
+using Entities.Contracts;
+
+namespace Entities.DTO
+{
+	public class ExamQuestionDto
+	{
+		public Guid Id { get; set; } = Guid.NewGuid();
+		
+		public string Title { get; set; } = string.Empty;
+
+		public float Score { get; set; } = 0;
+
+		public byte Index { get; set; } = 0;
+
+		public string Sequence { get; set; } = string.Empty;
+
+
+		public Guid QuestionTypeId { get; set; } 
+		
+		//public Guid? QuestionId { get; set; }
+
+		//public Guid? ParentExamQuestionId { get; set; }
+
+		public QuestionDto? Question { get; set; } 
+
+		//public ExamQuestionDto? ParentExamQuestion { get; set; }
+
+		public ICollection<ExamQuestionDto> ChildExamQuestions { get; set; } = new List<ExamQuestionDto>();
+
+		// public Layout Layout { get; set; } = Layout.horizontal;
+		// public QuestionContextDto? Description { get; set; }
+	}
+}