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

Entities/Contracts/SubmissionDetail.cs

@@ -20,15 +20,20 @@ namespace Entities.Contracts
 		[Column("submission_id")]
 		[ForeignKey("Submission")]
 		public Guid SubmissionId { get; set; }
+		[ForeignKey(nameof(SubmissionId))]
+		public virtual Submission Submission { get; set; }
 
 		[Required]
 		[Column("student_id")]
 		public Guid StudentId { get; set; }
+		[ForeignKey(nameof(StudentId))]
+		public virtual User Student { get; set; }
 
 		[Required]
-		[Column("assignment_question_id")]
-		[ForeignKey("AssignmentQuestion")]
-		public Guid AssignmentQuestionId { get; set; }
+		[Column("exam_question_id")]
+		public Guid ExamQuestionId { get; set; }
+		[ForeignKey(nameof(ExamQuestionId))]
+		public virtual ExamQuestion ExamQuestion { get; set; }
 
 		[Column("student_answer")]
 		public string? StudentAnswer { get; set; }
@@ -37,7 +42,7 @@ namespace Entities.Contracts
 		public bool? IsCorrect { get; set; }
 
 		[Column("points_awarded")]
-		public float? PointsAwarded { get; set; } // score
+		public float? PointsAwarded { get; set; } // 得分
 
 		[Column("teacher_feedback")]
 		public string? TeacherFeedback { get; set; }
@@ -51,20 +56,6 @@ namespace Entities.Contracts
 		[Column("deleted")]
 		public bool IsDeleted { get; set; }
 
-		[Required]
-		[Column("status")]
-		public SubmissionStatus Status { get; set; }
-
-
-
-		[ForeignKey(nameof(StudentId))]
-		public User Student { get; set; }
-
-		[ForeignKey(nameof(SubmissionId))]
-		public Submission Submission { get; set; }
-
-		[ForeignKey(nameof(AssignmentQuestionId))]
-		public AssignmentQuestion AssignmentQuestion { get; set; }
 
 		public SubmissionDetail()
 		{