重构作业结构：优化实体模型、DTO映射和前端界面

- 重构AppMainStruct、AssignmentQuestion、Question等实体模型
- 更新相关DTO以匹配新的数据结构
- 优化前端页面布局和组件
- 添加全局信息和笔记功能相关代码
- 更新数据库迁移和程序配置

Entities/Contracts/Global.cs

@@ -0,0 +1,24 @@
+using System;
+using System.Collections.Generic;
+using System.ComponentModel.DataAnnotations.Schema;
+using System.ComponentModel.DataAnnotations;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace Entities.Contracts
+{
+	[Table("global")]
+	public class Global
+	{
+		[Key]
+		[Column("id")]
+		public Guid Id { get; set; } = Guid.NewGuid();
+
+		public SubjectAreaEnum Area { get; set; }
+
+		public string Info { get; set; } = string.Empty;
+	}
+
+
+}