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

Entities/DTO/Submission/StudentSubmissionDetailDto.cs

@@ -0,0 +1,41 @@
+using Entities.Contracts;
+using System;
+using System.Collections.Generic;
+
+namespace Entities.DTO
+{
+    public class StudentSubmissionDetailDto
+    {
+        // 基本信息
+        public Guid Id { get; set; }
+        public Guid AssignmentId { get; set; }
+        public Guid StudentId { get; set; }
+        public DateTime SubmissionTime { get; set; }
+        public float OverallGrade { get; set; }
+        public string OverallFeedback { get; set; } = string.Empty;
+        public SubmissionStatus Status { get; set; }
+        
+        // Assignment信息
+        public ExamDto Assignment { get; set; } = new ExamDto();
+        
+        // 错误分析
+        public Dictionary<string, int> ErrorTypeDistribution { get; set; } = new Dictionary<string, int>();
+        public Dictionary<string, float> ErrorTypeScoreDistribution { get; set; } = new Dictionary<string, float>();
+        
+        // 成绩统计
+        public int TotalRank { get; set; }
+        public List<float> AllScores { get; set; } = new List<float>();
+        public float AverageScore { get; set; }
+        public float ClassAverageScore { get; set; }
+        
+        // 课文分布
+        public Dictionary<string, int> LessonErrorDistribution { get; set; } = new Dictionary<string, int>();
+        public Dictionary<string, int> KeyPointErrorDistribution { get; set; } = new Dictionary<string, int>();
+        
+        // 基础统计
+        public int TotalQuestions { get; set; }
+        public int CorrectCount { get; set; }
+        public int ErrorCount { get; set; }
+        public float AccuracyRate { get; set; }
+    }
+}