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

Entities/DTO/Submission/SubmissionListDto.cs

@@ -0,0 +1,22 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace Entities.DTO
+{
+	public record SubmissionListDto
+	{
+		public Guid Id { get; init; }
+
+
+		public float OverallGrade { get; init; }
+		public int ErrorCount { get; init; }
+		public Dictionary<string, int>? ErrorQuestionTypeDistribution { get; init; }
+		public Dictionary<string, int>? ErrorQuestionLessonDistribution { get; init; }
+
+
+		public byte AttemptNumber { get; init; }
+	}
+}