feat(调度任务): 实现调度任务管理功能

新增调度任务模块，支持任务的增删改查、启停及手动执行
- 后端添加 schedule_job 模型、服务、路由及调度器工具类
- 前端新增调度任务管理页面
- 修改 flow 相关接口将 id 类型从 String 改为 i64
- 添加 tokio-cron-scheduler 依赖实现定时任务调度
- 初始化时加载已启用任务并注册到调度器

backend/src/utils/scheduler.rs

@@ -0,0 +1,99 @@
+use std::collections::HashMap;
+use std::future::Future;
+use std::pin::Pin;
+use std::sync::Arc;
+use once_cell::sync::OnceCell;
+use tokio::sync::Mutex;
+use tokio_cron_scheduler::{JobScheduler, Job};
+use tracing::{error, info};
+use uuid::Uuid;
+
+use crate::models::schedule_job;
+
+static SCHEDULER: OnceCell<Mutex<JobScheduler>> = OnceCell::new();
+static JOB_GUIDS: OnceCell<Mutex<HashMap<String, Uuid>>> = OnceCell::new();
+
+pub type JobExecutor = Arc<dyn Fn() -> Pin<Box<dyn Future<Output = ()> + Send>> + Send + Sync>;
+
+fn scheduler() -> &'static Mutex<JobScheduler> {
+    SCHEDULER
+        .get()
+        .expect("Scheduler not initialized. Call init_and_start() early in main.")
+}
+
+fn job_guids() -> &'static Mutex<HashMap<String, Uuid>> {
+    JOB_GUIDS
+        .get()
+        .expect("JOB_GUIDS not initialized. Call init_and_start() early in main.")
+}
+
+pub async fn init_and_start() -> anyhow::Result<()> {
+    if SCHEDULER.get().is_some() {
+        return Ok(());
+    }
+    let js = JobScheduler::new().await?;
+    SCHEDULER.set(Mutex::new(js)).ok().expect("set scheduler once");
+    JOB_GUIDS.set(Mutex::new(HashMap::new())).ok().expect("set job_guids once");
+
+    // 仅启动调度器，不进行任何数据库加载，数据库加载应由 service 层负责
+    let lock = scheduler().lock().await;
+    lock.start().await?;
+    drop(lock);
+    info!(target = "udmin", "scheduler started");
+    Ok(())
+}
+
+/// 新增或更新一个任务（根据 model.id 作为唯一标识）。
+/// - 如果已存在，则先移除旧任务再按最新 cron 重新创建；
+/// - 当 enabled=false 时，仅执行移除逻辑，不会重新添加。
+pub async fn add_or_update_job_by_model(m: &schedule_job::Model, executor: JobExecutor) -> anyhow::Result<()> {
+    // 如果已有旧的 job，先移除
+    if let Some(old) = { job_guids().lock().await.get(&m.id).cloned() } {
+        let js = scheduler().lock().await;
+        if let Err(e) = js.remove(&old).await {
+            error!(target = "udmin", id = %m.id, guid = %old, error = %e, "scheduler.remove old failed");
+        }
+        job_guids().lock().await.remove(&m.id);
+    }
+
+    if !m.enabled {
+        return Ok(());
+    }
+
+    // 构造异步 Job（仅负责调度触发，不做数据库操作）
+    let cron_expr = m.cron_expr.clone();
+    let name = m.name.clone();
+    let job_id = m.id.clone();
+    let exec_arc = executor.clone();
+
+    let job = Job::new_async(cron_expr.as_str(), move |_uuid, _l| {
+        let job_name = name.clone();
+        let job_id = job_id.clone();
+        let exec = exec_arc.clone();
+        Box::pin(async move {
+            info!(target = "udmin", job = %job_name, id = %job_id, "scheduler.tick: start");
+            exec().await;
+        })
+    })?;
+
+    let guid = job.guid();
+    {
+        let js = scheduler().lock().await;
+        js.add(job).await?;
+    }
+    job_guids().lock().await.insert(m.id.clone(), guid);
+    info!(target = "udmin", id = %m.id, guid = %guid, "scheduler.add: ok");
+    Ok(())
+}
+
+pub async fn remove_job_by_id(id: &str) -> anyhow::Result<()> {
+    if let Some(g) = { job_guids().lock().await.get(id).cloned() } {
+        let js = scheduler().lock().await;
+        if let Err(e) = js.remove(&g).await {
+            error!(target = "udmin", id = %id, guid = %g, error = %e, "scheduler.remove: failed");
+        }
+        job_guids().lock().await.remove(id);
+        info!(target = "udmin", id = %id, guid = %g, "scheduler.remove: ok");
+    }
+    Ok(())
+}