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

Entities/DTO/Class/ClassResponseDto.cs

@@ -0,0 +1,22 @@
+using Entities.Contracts;
+using System;
+using System.Collections.Generic;
+
+namespace Entities.DTO
+{
+    public class ClassResponseDto
+    {
+        public Guid Id { get; set; }
+        public Guid GradeId { get; set; }
+        public string GradeName { get; set; }
+        public string ClassName { get; set; }
+        public Guid? HeadTeacherId { get; set; }
+        public string HeadTeacherName { get; set; }
+        public DateTime CreatedAt { get; set; }
+        public DateTime UpdatedAt { get; set; }
+        public bool IsDeleted { get; set; }
+
+        // Navigation properties for response
+        public ICollection<ClassUserDto> ClassStudents { get; set; }
+    }
+}