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

Entities/Contracts/ExamQuestion.cs

@@ -0,0 +1,71 @@
+using System.ComponentModel.DataAnnotations.Schema;
+using System.ComponentModel.DataAnnotations;
+using Entities.DTO;
+
+namespace Entities.Contracts
+{
+	[Table("exam_questions")]
+	public class ExamQuestion
+	{
+		[Key]
+		[Column("id")]
+		public Guid Id { get; set; }
+
+		[Column("title")]
+		[MaxLength(1024)]
+		public string? Title { get; set; }
+
+		[Column("question_id")]
+		public Guid? QuestionId { get; set; }
+		[ForeignKey(nameof(QuestionId))]
+		public virtual Question? Question { get; set; }
+
+		[Column("description")]
+		public Guid? QuestionContextId { get; set; }
+		[ForeignKey(nameof(QuestionContextId))]
+		public virtual QuestionContext? QuestionContext { get; set; }
+
+		[Required]
+		[Column("question_number")]
+		public byte Index { get; set; }
+
+		[Column("sequence")]
+		public string Sequence { get; set; } = string.Empty;
+
+		[Column("parent_question_group_id")]
+		public Guid? ParentExamQuestionId { get; set; }
+		[ForeignKey(nameof(ParentExamQuestionId))]
+		public virtual ExamQuestion? ParentExamQuestion { get; set; }
+
+		public Guid QuestionTypeId { get;set; }
+		[ForeignKey(nameof(QuestionTypeId))]
+		public virtual QuestionType Type { get; set; }
+
+		[Column("created_at")]
+		public DateTime CreatedAt { get; set; }
+
+		[Column("exam_struct_type")]
+		public ExamStructType ExamStructType { get; set; }
+		
+		[Column("score")]
+		public float? Score { get; set; }
+
+		[Column("deleted")]
+		public bool IsDeleted { get; set; }
+
+
+		public virtual Exam? Exam { get; set; }
+
+
+		[InverseProperty(nameof(SubmissionDetail.ExamQuestion))]
+		public virtual ICollection<SubmissionDetail> SubmissionDetails { get; set; }
+		[InverseProperty(nameof(ParentExamQuestion))]
+		public virtual ICollection<ExamQuestion> ChildExamQuestions { get; set; } = new List<ExamQuestion>();
+
+		public ExamQuestion()
+		{
+			Id = Guid.NewGuid();
+			SubmissionDetails = new HashSet<SubmissionDetail>();
+		}
+	}
+}