feat(jobs): 提交后回填补偿落库 backfill_todo 并到期重试 (ACM2-29 P2-3)

- V1.3.2 迁移：backfill_todo 持久补偿表（attempts/next_attempt_at/last_error）
- BackfillTodoRepository 接口 + PG 实现与 stub；record 幂等 upsert
- BackfillSweepJob：到期重试，成功即删，失败指数退避（30s 起步封顶 15 分钟）；
  触发点 = InboxPoller 每轮心跳（重启即对账）+ JobExecutor BACKFILL_SWEEP 类型
- MessageProcessor/SnapshotFlow 回填失败落待办（成功终态不降级，业务不重放）；
  SKIPPED 重复报文同样补偿共享信箱回填，防止重复信件被反复轮询
- 新测试：扫描重试/退避/恢复对账 4 用例；快照回填失败落库断言；
  跳过路径补偿落库断言

验证：MSGX_PG_PORT=5433 真实 PG 全量 102 用例 0 失败 0 跳过 (ACM2-29)

src/main/kotlin/com/gzzn/omms/msgexchange/processing/SnapshotFlow.kt

@@ -8,6 +8,7 @@ import com.gzzn.omms.msgexchange.domain.ProcStatus
 import com.gzzn.omms.msgexchange.domain.MsgEvent
 import com.gzzn.omms.msgexchange.domain.MsgKind
 import com.gzzn.omms.msgexchange.domain.Targets
+import com.gzzn.omms.msgexchange.infra.persistence.BackfillTodoRepository
 import com.gzzn.omms.msgexchange.infra.persistence.CminmsgInboxRepository
 import com.gzzn.omms.msgexchange.infra.persistence.FlightFields
 import com.gzzn.omms.msgexchange.infra.persistence.FlightFieldsJson
@@ -33,6 +34,7 @@ class SnapshotFlow(
     private val procFailure: ProcFailure,
     private val txManager: PipelineTransactionManager,
     private val inbox: CminmsgInboxRepository,
+    private val backfillTodo: BackfillTodoRepository? = null,
 ) {
     private val log = org.slf4j.LoggerFactory.getLogger(SnapshotFlow::class.java)
 
@@ -139,6 +141,16 @@ class SnapshotFlow(
             inbox.backfillOnSuccess(head.cminmsgsId, msg.meta.sndr, msg.meta.type, msg.meta.styp, msg.meta.seqn)
         } catch (e: Exception) {
             log.error("backfill failed after SUCCEEDED id={} (compensation required)", head.cminmsgsId, e)
+            backfillTodo?.record(
+                BackfillTodoRepository.BackfillTask(
+                    cminmsgsId = head.cminmsgsId,
+                    sndr = msg.meta.sndr,
+                    type = msg.meta.type,
+                    styp = msg.meta.styp,
+                    seqn = msg.meta.seqn,
+                ),
+                e.message ?: e.javaClass.simpleName,
+            ) ?: log.warn("no backfill-todo repository bound; compensation NOT persisted id={}", head.cminmsgsId)
         }
     }