feat: 添加学生提交系统功能

- 添加学生提交管理服务 (StudentSubmissionService, StudentSubmissionDetailService)
- 新增学生提交相关控制器 (StudentSubmissionController, StudentSubmissionDetailController)
- 添加学生提交数据传输对象 (StudentSubmissionDetailDto, StudentSubmissionSummaryDto)
- 新增学生提交相关页面组件 (StudentExamView, ExamDetailView, StudentCard等)
- 添加学生提交信息卡片组件 (SubmissionInfoCard, TeacherSubmissionInfoCard)
- 更新数据库迁移文件以支持提交系统

Entities/DTO/StudentSubmissionSummaryDto.cs

@@ -0,0 +1,22 @@
+using System;
+
+namespace Entities.DTO
+{
+    public class StudentSubmissionSummaryDto
+    {
+        public Guid Id { get; set; }
+        public string AssignmentName { get; set; }
+        public int ErrorCount { get; set; }
+        public DateTime CreatedDate { get; set; }
+        public float Score { get; set; }
+        public int TotalQuestions { get; set; }
+        public string StudentName { get; set; }
+        public string Status { get; set; }
+    }
+
+    public class StudentSubmissionSummaryResponseDto
+    {
+        public List<StudentSubmissionSummaryDto> Submissions { get; set; }
+        public int TotalCount { get; set; }
+    }
+}