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

Entities/DTO/Exam/AssigExamToStudentsDto.cs

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+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace Entities.DTO
+{
+	public class AssigExamToStudentsDto
+	{
+		public Guid CreaterId { get; set; }
+		public Guid ExamId { get; set; }
+		public Guid ClassId { get; set; }
+		public List<Guid> StudentIds { get; set; } = new List<Guid>();
+	}
+
+	public record AssigExamToClassDto(Guid examId, Guid classId);
+}

Entities/DTO/Exam/AssignmentClassDto.cs

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+using Entities.Contracts;
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+using System.Xml.Serialization;
+
+namespace Entities.DTO
+{
+
+
+	public class AssignmentClassDto
+	{
+		public ExamDto Assignment { get; set; }
+		public ClassDto ClassId { get; set; }
+		public DateTime AssignedAt { get; set; }
+	}
+
+
+
+
+}

Entities/DTO/Exam/CreateExamDto.cs

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+using System;
+using System.ComponentModel.DataAnnotations;
+
+namespace Entities.DTO
+{
+    public class CreateExamDto
+    {
+        [Required(ErrorMessage = "考试标题是必填项。")]
+        [StringLength(255, ErrorMessage = "考试标题不能超过 255 个字符。")]
+        public string Title { get; set; }
+
+        public string Description { get; set; }
+
+        [Required(ErrorMessage = "科目ID是必填项。")]
+        public Guid SubjectId { get; set; }
+
+        [Required(ErrorMessage = "考试结构ID是必填项。")]
+        public Guid ExamStructId { get; set; }
+
+        [Required(ErrorMessage = "考试类型ID是必填项。")]
+        public Guid ExamTypeId { get; set; }
+
+        [Required(ErrorMessage = "创建者ID是必填项。")]
+        public Guid CreatorId { get; set; }
+
+        [Required(ErrorMessage = "截止日期是必填项。")]
+        public DateTime DueDate { get; set; }
+
+        public byte TotalQuestions { get; set; }
+
+        public float Score { get; set; }
+
+        public string Name { get; set; }
+    }
+}

Entities/DTO/Exam/ExamDto.cs

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+using Entities.Contracts;
+using System;
+using System.ComponentModel.DataAnnotations;
+
+namespace Entities.DTO
+{
+    public class ExamDto
+    {
+        public Guid Id { get; set; } = Guid.NewGuid();
+
+        [Required(ErrorMessage = "考试标题是必填项。")]
+        [StringLength(255, ErrorMessage = "考试标题不能超过 255 个字符。")]
+        public string Title { get; set; }
+
+        public string Description { get; set; }
+
+		public byte TotalQuestions { get; set; }
+
+		public float Score { get; set; }
+
+		public string Name { get; set; }
+
+
+
+
+
+		[Required(ErrorMessage = "截止日期是必填项。")]
+		public DateTime DueDate { get; set; }
+
+		public Guid SubjectId { get; set; }
+
+        public Guid ExamTypeId { get; set; }
+
+        public Guid CreatorId { get; set; }
+
+		//public Guid ExamStructId { get; set; } 
+
+
+		public ExamQuestionDto ExamStruct { get; set; } = new ExamQuestionDto();
+
+        public DateTime CreatedAt { get; set; }
+        public DateTime UpdatedAt { get; set; }
+    }
+}

Entities/DTO/Exam/ExamListDto.cs

@@ -0,0 +1,10 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace Entities.DTO
+{
+	public record ExamListDto(Guid Id, string Name);
+}

Entities/DTO/Exam/ExamQuestionDto.cs

@@ -0,0 +1,33 @@
+using Entities.Contracts;
+
+namespace Entities.DTO
+{
+	public class ExamQuestionDto
+	{
+		public Guid Id { get; set; } = Guid.NewGuid();
+		
+		public string Title { get; set; } = string.Empty;
+
+		public float Score { get; set; } = 0;
+
+		public byte Index { get; set; } = 0;
+
+		public string Sequence { get; set; } = string.Empty;
+
+
+		public Guid QuestionTypeId { get; set; } 
+		
+		//public Guid? QuestionId { get; set; }
+
+		//public Guid? ParentExamQuestionId { get; set; }
+
+		public QuestionDto? Question { get; set; } 
+
+		//public ExamQuestionDto? ParentExamQuestion { get; set; }
+
+		public ICollection<ExamQuestionDto> ChildExamQuestions { get; set; } = new List<ExamQuestionDto>();
+
+		// public Layout Layout { get; set; } = Layout.horizontal;
+		// public QuestionContextDto? Description { get; set; }
+	}
+}

Entities/DTO/Exam/ExamResponseDto.cs

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+using System;
+using System.Collections.Generic;
+
+namespace Entities.DTO
+{
+    public class ExamResponseDto
+    {
+        public Guid Id { get; set; }
+        public string Title { get; set; }
+        public string Description { get; set; }
+        public Guid SubjectId { get; set; }
+        public string SubjectName { get; set; }
+        public Guid ExamStructId { get; set; }
+        public string ExamStructName { get; set; }
+        public Guid ExamTypeId { get; set; }
+        public string ExamTypeName { get; set; }
+        public Guid CreatorId { get; set; }
+        public string CreatorName { get; set; }
+        public DateTime DueDate { get; set; }
+        public byte TotalQuestions { get; set; }
+        public float Score { get; set; }
+        public string Name { get; set; }
+        public DateTime CreatedAt { get; set; }
+        public DateTime UpdatedAt { get; set; }
+        public bool IsDeleted { get; set; }
+
+        // Navigation properties for response
+        public int AttachmentCount { get; set; }
+        public int SubmissionCount { get; set; }
+        public List<string> AttachmentNames { get; set; } = new List<string>();
+        public List<string> StudentNames { get; set; } = new List<string>();
+        public List<DateTime> SubmissionTimes { get; set; } = new List<DateTime>();
+    }
+}

Entities/DTO/Exam/UpdateExamDto.cs

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+using System;
+using System.ComponentModel.DataAnnotations;
+
+namespace Entities.DTO
+{
+    public class UpdateExamDto
+    {
+        [Required(ErrorMessage = "考试ID是必填项。")]
+        public Guid Id { get; set; }
+
+        [Required(ErrorMessage = "考试标题是必填项。")]
+        [StringLength(255, ErrorMessage = "考试标题不能超过 255 个字符。")]
+        public string Title { get; set; }
+
+        public string Description { get; set; }
+
+        [Required(ErrorMessage = "科目ID是必填项。")]
+        public Guid SubjectId { get; set; }
+
+        [Required(ErrorMessage = "考试结构ID是必填项。")]
+        public Guid ExamStructId { get; set; }
+
+        [Required(ErrorMessage = "考试类型ID是必填项。")]
+        public Guid ExamTypeId { get; set; }
+
+        [Required(ErrorMessage = "创建者ID是必填项。")]
+        public Guid CreatorId { get; set; }
+
+        [Required(ErrorMessage = "截止日期是必填项。")]
+        public DateTime DueDate { get; set; }
+
+        public byte TotalQuestions { get; set; }
+
+        public float Score { get; set; }
+
+        public string Name { get; set; }
+    }
+}