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

TechHelper.Server/Context/Configuration/AssignmentConfiguration.cs

@@ -5,9 +5,9 @@ using Microsoft.EntityFrameworkCore.Metadata.Builders;
 
 namespace TechHelper.Context.Configuration
 {
-	public class AssignmentConfiguration : IEntityTypeConfiguration<Assignment>
+	public class AssignmentConfiguration : IEntityTypeConfiguration<Exam>
 	{
-		public void Configure(EntityTypeBuilder<Assignment> builder)
+		public void Configure(EntityTypeBuilder<Exam> builder)
 		{
 			builder.ToTable("assignments");
 
@@ -61,7 +61,7 @@ namespace TechHelper.Context.Configuration
 
 			builder.HasOne(a=>a.ExamStruct)
 				.WithOne()
-				.HasForeignKey<Assignment>(a=>a.ExamStructId)
+				.HasForeignKey<Exam>(a=>a.ExamStructId)
 				.OnDelete(DeleteBehavior.Cascade);
 
 		}