Version: 0.9.69.dev.260504

后端：
1. 阶段 4 active-scheduler 服务边界落地，新增 `cmd/active-scheduler`、`services/active_scheduler`、`shared/contracts/activescheduler` 和 active-scheduler port，迁移 dry-run、trigger、preview、confirm zrpc 能力
2. active-scheduler outbox consumer、relay、retry loop 和 due job scanner 迁入独立服务入口，gateway `/active-schedule/*` 改为通过 zrpc client 调用
3. gateway 目录收口为 `gateway/api` + `gateway/client`，统一归档 userauth、notification、active-scheduler 的 HTTP 门面和 zrpc client
4. 将旧 `backend/active_scheduler` 领域核心下沉到 `services/active_scheduler/core`，清退旧根目录活跃实现，并补充 active-scheduler 启动期跨域依赖表检查
5. 调整单体启动与 outbox 归属，`cmd/all` 不再启动 active-scheduler workflow、scanner 或 handler

文档：
1. 更新微服务迁移计划，将阶段 4 active-scheduler 标记为首轮收口完成，并明确下一阶段进入 schedule / task / course / task-class

backend/services/active_scheduler/rpc/active_scheduler.proto

@@ -0,0 +1,53 @@
+syntax = "proto3";
+
+package smartflow.active_scheduler;
+
+option go_package = "github.com/LoveLosita/smartflow/backend/services/active_scheduler/rpc/pb";
+
+service ActiveScheduler {
+  rpc DryRun(ActiveScheduleRequest) returns (JSONResponse);
+  rpc Trigger(ActiveScheduleRequest) returns (TriggerResponse);
+  rpc CreatePreview(ActiveScheduleRequest) returns (JSONResponse);
+  rpc GetPreview(GetPreviewRequest) returns (JSONResponse);
+  rpc ConfirmPreview(ConfirmPreviewRequest) returns (JSONResponse);
+}
+
+message ActiveScheduleRequest {
+  int64 user_id = 1;
+  string trigger_type = 2;
+  string target_type = 3;
+  int64 target_id = 4;
+  string feedback_id = 5;
+  string idempotency_key = 6;
+  int64 mock_now_unix_nano = 7;
+  bytes payload_json = 8;
+}
+
+message GetPreviewRequest {
+  int64 user_id = 1;
+  string preview_id = 2;
+}
+
+message ConfirmPreviewRequest {
+  int64 user_id = 1;
+  string preview_id = 2;
+  string candidate_id = 3;
+  string action = 4;
+  bytes edited_changes_json = 5;
+  string idempotency_key = 6;
+  int64 requested_at_unix_nano = 7;
+  string trace_id = 8;
+}
+
+message JSONResponse {
+  bytes data_json = 1;
+}
+
+message TriggerResponse {
+  string trigger_id = 1;
+  string status = 2;
+  string preview_id = 3;
+  bool has_preview_id = 4;
+  bool dedupe_hit = 5;
+  string trace_id = 6;
+}