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

Entities/DTO/Question/QuestionDto.cs

@@ -0,0 +1,36 @@
+using Entities.Contracts;
+
+namespace Entities.DTO
+{
+	public class QuestionDto
+	{
+		public Guid Id { get; set; } = Guid.NewGuid();
+
+		public string Title { get; set; } = string.Empty;
+
+		public string? Answer { get; set; } = string.Empty;
+
+		public string? Options { get; set; }
+
+		//public DifficultyLevel DifficultyLevel { get; set; } = DifficultyLevel.easy;
+
+
+
+		public Guid QuestioTypeId { get; set; } 
+
+		public Guid SubjectId { get; set; }
+
+		//public Guid CreatorId { get; set; }
+
+		public Guid? KeyPointId { get; set; }
+
+		public Guid? LessonId { get; set; }
+
+
+
+		public DateTime CreatedAt { get; set; }
+
+		public DateTime UpdatedAt { get; set; } = DateTime.Now;
+
+	}
+}