feat(scheduler): 引入调度快照缓存与 outbox 回放

- 调度热路径优先读 Redis 快照，保留分组排序语义
- outbox 回放 + 全量重建纠偏，失败重试不推进水位
- 自动 Atlas 基线对齐并同步调度配置示例

backend/internal/service/scheduler_events.go

@@ -0,0 +1,10 @@
+package service
+
+const (
+	SchedulerOutboxEventAccountChanged       = "account_changed"
+	SchedulerOutboxEventAccountGroupsChanged = "account_groups_changed"
+	SchedulerOutboxEventAccountBulkChanged   = "account_bulk_changed"
+	SchedulerOutboxEventAccountLastUsed      = "account_last_used"
+	SchedulerOutboxEventGroupChanged         = "group_changed"
+	SchedulerOutboxEventFullRebuild          = "full_rebuild"
+)