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

TechHelper.Server/Repository/LessonRepository.cs

@@ -0,0 +1,18 @@
+using Entities.Contracts;
+using SharedDATA.Api;
+using System.Linq.Expressions;
+using TechHelper.Context;
+using TechHelper.Server.Repository;
+
+namespace TechHelper.Server.Repository
+{
+    /// <summary>
+    /// Lesson仓储实现类
+    /// </summary>
+    public class LessonRepository : Repository<Lesson>, IRepository<Lesson>
+    {
+		public LessonRepository(ApplicationContext context) : base(context)
+		{
+		}
+	}
+}