feat: 添加学生提交系统功能

- 添加学生提交管理服务 (StudentSubmissionService, StudentSubmissionDetailService)
- 新增学生提交相关控制器 (StudentSubmissionController, StudentSubmissionDetailController)
- 添加学生提交数据传输对象 (StudentSubmissionDetailDto, StudentSubmissionSummaryDto)
- 新增学生提交相关页面组件 (StudentExamView, ExamDetailView, StudentCard等)
- 添加学生提交信息卡片组件 (SubmissionInfoCard, TeacherSubmissionInfoCard)
- 更新数据库迁移文件以支持提交系统

TechHelper.Server/Migrations/ApplicationContextModelSnapshot.cs

@@ -175,6 +175,9 @@ namespace TechHelper.Server.Migrations
                     b.Property<Guid?>("AssignmentId")
                         .HasColumnType("char(36)");
 
+                    b.Property<bool>("BCorrect")
+                        .HasColumnType("tinyint(1)");
+
                     b.Property<DateTime>("CreatedAt")
                         .HasColumnType("datetime(6)")
                         .HasColumnName("created_at");
@@ -558,7 +561,7 @@ namespace TechHelper.Server.Migrations
                         .HasColumnType("longtext")
                         .HasColumnName("overall_feedback");
 
-                    b.Property<float?>("OverallGrade")
+                    b.Property<float>("OverallGrade")
                         .HasPrecision(5, 2)
                         .HasColumnType("float")
                         .HasColumnName("overall_grade");
@@ -800,19 +803,19 @@ namespace TechHelper.Server.Migrations
                     b.HasData(
                         new
                         {
-                            Id = new Guid("8c6c5e8e-ef00-444c-9c7c-cba5cd6f7043"),
+                            Id = new Guid("d480cdca-7de2-4abe-8129-73bbaa6c1b32"),
                             Name = "Student",
                             NormalizedName = "STUDENT"
                         },
                         new
                         {
-                            Id = new Guid("2670f35a-df0c-4071-8879-80eb99d138a1"),
+                            Id = new Guid("d7bcfb37-3f1c-467b-a3f0-b2339a8a990d"),
                             Name = "Teacher",
                             NormalizedName = "TEACHER"
                         },
                         new
                         {
-                            Id = new Guid("9eda9d90-0cd2-4fbe-b07e-f90bd01f32db"),
+                            Id = new Guid("f4a6788a-04d8-499c-9e64-73dfba97ca6b"),
                             Name = "Administrator",
                             NormalizedName = "ADMINISTRATOR"
                         });