1. 教室容量按 1/2 计算

- ExamArrangementService.cs: SelectRooms() 使用 Capacity / 2 选择房间、计算剩余座位和总容量
  - MakeupExamArrangementService.cs: 数据库查询用 x.Capacity >= enrolledCount * 2（等价于 Capacity/2 >=
  enrolledCount），消息显示有效座位数

  2. 教学楼限制多选

  - Domain: ExamSession 和 MakeupExamSession 新增 RequiredBuildingIds (JSON string)，保留旧 RequiredBuildingId 向后兼容
  - Service: RoomGroupKey 改为字符串键确保值相等；GroupKey() 合并新旧字段
  - Controller: 请求 DTO 增加 RequiredBuildingIds (Guid 数组)，响应包含该字段
  - DB: MySQL 迁移 + SQLite migrator 添加新列
  - Frontend: <el-select> 改为 multiple，新增 parseBuildingIds() 解析服务器返回的 JSON

  3. 导出签名单后台任务

  - 新增: ExamSignInExportJob 实体、ExamSignInExportJobProcessor、ExamSignInExportJobStatus 枚举
  - BackgroundJobKind: 新增 ExamSignInExport = 5
  - RabbitMQ: routing key exam.sign-in-export，队列 jiaowu.background-jobs.exam.sign-in-export
  - API: POST /sign-in-export 创建任务返回 202；GET /sign-in-exports/{jobId} 查询状态；GET
  /sign-in-exports/{jobId}/download 下载文件
  - Frontend: 导出改为异步任务 + 轮询 + 自动下载，显示进度条
  - 恢复: OutboxPublisher 启动时恢复未完成的任务，重试超限自动标记失败

src/Jiaowu.Api/Infrastructure/Persistence/Migrations/MySql/AppDbContextModelSnapshot.cs

@@ -1778,6 +1778,9 @@ namespace Jiaowu.Api.Infrastructure.Persistence.Migrations.MySql
                     b.Property<Guid?>("RequiredBuildingId")
                         .HasColumnType("char(36)");
 
+                    b.Property<string>("RequiredBuildingIds")
+                        .HasColumnType("longtext");
+
                     b.Property<int>("RequiredInvigilatorCount")
                         .HasColumnType("int");
 
@@ -1823,6 +1826,62 @@ namespace Jiaowu.Api.Infrastructure.Persistence.Migrations.MySql
                     b.ToTable("ExamSessionInvigilators");
                 });
 
+            modelBuilder.Entity("Jiaowu.Api.Domain.Academic.ExamSignInExportJob", b =>
+                {
+                    b.Property<Guid>("Id")
+                        .ValueGeneratedOnAdd()
+                        .HasColumnType("char(36)");
+
+                    b.Property<DateTime?>("CompletedAt")
+                        .HasColumnType("datetime(6)");
+
+                    b.Property<DateTime>("CreatedAt")
+                        .HasColumnType("datetime(6)");
+
+                    b.Property<string>("CurrentStep")
+                        .HasMaxLength(200)
+                        .HasColumnType("varchar(200)");
+
+                    b.Property<string>("ErrorMessage")
+                        .HasMaxLength(2000)
+                        .HasColumnType("varchar(2000)");
+
+                    b.Property<byte[]>("FileBytes")
+                        .HasColumnType("longblob");
+
+                    b.Property<string>("FileName")
+                        .HasMaxLength(200)
+                        .HasColumnType("varchar(200)");
+
+                    b.Property<int>("FileSize")
+                        .HasColumnType("int");
+
+                    b.Property<Guid>("PlanId")
+                        .HasColumnType("char(36)");
+
+                    b.Property<Guid?>("RequestedByUserId")
+                        .HasColumnType("char(36)");
+
+                    b.Property<DateTime?>("StartedAt")
+                        .HasColumnType("datetime(6)");
+
+                    b.Property<int>("Status")
+                        .HasColumnType("int");
+
+                    b.Property<DateTime>("UpdatedAt")
+                        .HasColumnType("datetime(6)");
+
+                    b.HasKey("Id");
+
+                    b.HasIndex("RequestedByUserId");
+
+                    b.HasIndex("PlanId", "CreatedAt");
+
+                    b.HasIndex("Status", "CreatedAt");
+
+                    b.ToTable("ExamSignInExportJobs");
+                });
+
             modelBuilder.Entity("Jiaowu.Api.Domain.Academic.GradeItem", b =>
                 {
                     b.Property<Guid>("Id")
@@ -2488,6 +2547,9 @@ namespace Jiaowu.Api.Infrastructure.Persistence.Migrations.MySql
                     b.Property<Guid?>("RequiredBuildingId")
                         .HasColumnType("char(36)");
 
+                    b.Property<string>("RequiredBuildingIds")
+                        .HasColumnType("longtext");
+
                     b.Property<int>("RequiredInvigilatorCount")
                         .HasColumnType("int");