排课计算、课表发布、补考自动编排三类任务统一接入消息系统。

业务任务与 Outbox 消息同一事务落库，避免“数据库成功但消息没发出去”。
RabbitMQ 使用持久化消息、发布确认、手动 ACK、Quorum Queue、死信队列。
增加处理租约、心跳、异常重试、最大重试次数和幂等状态控制。
保留 InMemory 模式，开发环境无需安装 RabbitMQ。
支持多实例竞争消费，后续可以横向扩容。
新增 /health/messaging 消息系统健康检查。

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

@@ -0,0 +1,43 @@
+using Jiaowu.Api.Domain.Common;
+
+namespace Jiaowu.Api.Domain.System;
+
+public sealed class BackgroundJobOutboxMessage : EntityBase
+{
+    public BackgroundJobKind JobKind { get; set; }
+    public Guid JobId { get; set; }
+    public BackgroundJobOutboxState State { get; set; } =
+        BackgroundJobOutboxState.Pending;
+    public int PublishAttempts { get; set; }
+    public int ProcessingAttempts { get; set; }
+    public DateTime? PublishedAt { get; set; }
+    public Guid? ProcessingToken { get; set; }
+    public DateTime? LeaseExpiresAt { get; set; }
+    public DateTime? CompletedAt { get; set; }
+    public string? LastError { get; set; }
+
+    public static BackgroundJobOutboxMessage Create(
+        BackgroundJobKind jobKind,
+        Guid jobId) =>
+        new()
+        {
+            JobKind = jobKind,
+            JobId = jobId
+        };
+}
+
+public enum BackgroundJobKind
+{
+    AutomaticSchedule = 1,
+    SchedulePublish = 2,
+    MakeupExamAuto = 3
+}
+
+public enum BackgroundJobOutboxState
+{
+    Pending = 1,
+    Publishing = 2,
+    Published = 3,
+    Processing = 4,
+    Completed = 5
+}