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/Domain/Academic/ExamEntities.cs

@@ -63,6 +63,7 @@ public sealed class ExamSession : EntityBase
     public DateTime EndsAt { get; set; }
     public Guid? RequiredBuildingId { get; set; }
     public Building? RequiredBuilding { get; set; }
+    public string? RequiredBuildingIds { get; set; }
     public int RequiredInvigilatorCount { get; set; } = 2;
     public string? Notes { get; set; }
     public ICollection<ExamSessionInvigilator> Invigilators { get; set; } = [];

src/Jiaowu.Api/Domain/Academic/ExamSignInExportJob.cs

@@ -0,0 +1,26 @@
+using Jiaowu.Api.Domain.Common;
+
+namespace Jiaowu.Api.Domain.Academic;
+
+public sealed class ExamSignInExportJob : EntityBase
+{
+    public Guid PlanId { get; set; }
+    public ExamSignInExportJobStatus Status { get; set; } =
+        ExamSignInExportJobStatus.Queued;
+    public Guid? RequestedByUserId { get; set; }
+    public string? FileName { get; set; }
+    public byte[]? FileBytes { get; set; }
+    public int FileSize { get; set; }
+    public string? CurrentStep { get; set; }
+    public string? ErrorMessage { get; set; }
+    public DateTime? StartedAt { get; set; }
+    public DateTime? CompletedAt { get; set; }
+}
+
+public enum ExamSignInExportJobStatus
+{
+    Queued = 1,
+    Running = 2,
+    Succeeded = 3,
+    Failed = 4
+}

src/Jiaowu.Api/Domain/Academic/MakeupExamEntities.cs

@@ -28,6 +28,7 @@ public sealed class MakeupExamSession : EntityBase
     public DateTime EndsAt { get; set; }
     public Guid? RequiredBuildingId { get; set; }
     public Building? RequiredBuilding { get; set; }
+    public string? RequiredBuildingIds { get; set; }
     public int RequiredInvigilatorCount { get; set; } = 2;
     public string? Notes { get; set; }
     public ICollection<MakeupExamSessionInvigilator> Invigilators { get; set; } = [];

src/Jiaowu.Api/Domain/System/BackgroundJobOutboxMessage.cs

@@ -31,7 +31,8 @@ public enum BackgroundJobKind
     AutomaticSchedule = 1,
     SchedulePublish = 2,
     MakeupExamAuto = 3,
-    ExamArrangement = 4
+    ExamArrangement = 4,
+    ExamSignInExport = 5
 }
 
 public enum BackgroundJobOutboxState