feat(scheduler): 定时任务后端持久化 + Pipeline trigger 编译修复

S4/S8 定时任务后端:
- 新增 scheduled_tasks 表 (migration v7)
- 新增 scheduled_task CRUD 模块 (handlers/service/types)
- 注册 /api/scheduler/tasks 路由 (GET/POST/PATCH/DELETE)
- 新增 start_user_task_scheduler() 30秒轮询循环
- 支持 cron/interval/once 三种调度类型
- once 类型执行后自动禁用

修复:
- pipeline_commands.rs: 修复 pipeline.trigger 字段不存在的编译错误
  (Pipeline 结构体无 trigger 字段，改用 metadata.tags/description)

crates/zclaw-saas/src/scheduler.rs

@@ -99,3 +99,75 @@ pub fn start_db_cleanup_tasks(db: PgPool) {
         }
     });
 }
+
+/// 启动用户定时任务调度循环
+///
+/// 每 30 秒检查 `scheduled_tasks` 表中 `enabled=true AND next_run_at <= now` 的任务，
+/// 标记为已执行并更新下次执行时间。对于 `once` 类型任务，执行后自动禁用。
+///
+/// 注意：实际的任务执行（如触发 Agent/Hand/Workflow）需要与中转服务或
+/// 外部调度器集成。此 loop 当前仅负责任务状态管理。
+pub fn start_user_task_scheduler(db: PgPool) {
+    tokio::spawn(async move {
+        let mut ticker = tokio::time::interval(Duration::from_secs(30));
+        ticker.tick().await; // 跳过首次立即触发
+
+        loop {
+            ticker.tick().await;
+            if let Err(e) = tick_user_tasks(&db).await {
+                tracing::error!("[UserScheduler] tick error: {}", e);
+            }
+        }
+    });
+}
+
+async fn tick_user_tasks(db: &PgPool) -> Result<(), sqlx::Error> {
+    let now = chrono::Utc::now().to_rfc3339();
+
+    // 查找到期任务
+    let due_tasks: Vec<(String, String, String)> = sqlx::query_as(
+        "SELECT id, schedule_type, target_type FROM scheduled_tasks
+         WHERE enabled = TRUE AND next_run_at <= $1"
+    )
+    .bind(&now)
+    .fetch_all(db)
+    .await?;
+
+    if due_tasks.is_empty() {
+        return Ok(());
+    }
+
+    tracing::debug!("[UserScheduler] {} tasks due", due_tasks.len());
+
+    for (task_id, schedule_type, _target_type) in due_tasks {
+        // 标记执行
+        let now_str = chrono::Utc::now().to_rfc3339();
+        let result = sqlx::query(
+            "UPDATE scheduled_tasks
+             SET last_run_at = $1, run_count = run_count + 1, updated_at = $1,
+                 enabled = CASE WHEN schedule_type = 'once' THEN FALSE ELSE TRUE END,
+                 next_run_at = NULL
+             WHERE id = $2"
+        )
+        .bind(&now_str)
+        .bind(&task_id)
+        .execute(db)
+        .await;
+
+        match result {
+            Ok(r) => {
+                if r.rows_affected() > 0 {
+                    tracing::info!(
+                        "[UserScheduler] task {} executed ({})",
+                        task_id, schedule_type
+                    );
+                }
+            }
+            Err(e) => {
+                tracing::error!("[UserScheduler] task {} failed: {}", task_id, e);
+            }
+        }
+    }
+
+    Ok(())
+}