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

Entities/DTO/Subject/SubjectResponseDto.cs

@@ -0,0 +1,19 @@
+using System;
+using System.Collections.Generic;
+
+namespace Entities.DTO
+{
+    public class SubjectResponseDto
+    {
+        public Guid Id { get; set; }
+        public string Name { get; set; }
+        public string Description { get; set; }
+
+        // Navigation properties for response
+        public int QuestionTypeCount { get; set; }
+        public int QuestionCount { get; set; }
+        public int TeacherCount { get; set; }
+        public List<string> QuestionTypeNames { get; set; } = new List<string>();
+        public List<string> TeacherNames { get; set; } = new List<string>();
+    }
+}