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/Cargo.lock

@@ -661,6 +661,15 @@ dependencies = [
  "cfg-if",
 ]
 
+[[package]]
+name = "croner"
+version = "2.2.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "c344b0690c1ad1c7176fe18eb173e0c927008fdaaa256e40dfd43ddd149c0843"
+dependencies = [
+ "chrono",
+]
+
 [[package]]
 name = "crossbeam-queue"
 version = "0.3.12"
@@ -1763,6 +1772,17 @@ version = "0.1.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "51d515d32fb182ee37cda2ccdcb92950d6a3c2893aa280e540671c2cd0f3b1d9"
 
+[[package]]
+name = "num-derive"
+version = "0.4.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "ed3955f1a9c7c0c15e092f9c887db08b1fc683305fdf6eb6684f22555355e202"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "syn 2.0.106",
+]
+
 [[package]]
 name = "num-integer"
 version = "0.1.46"
@@ -3637,6 +3657,21 @@ dependencies = [
  "windows-sys 0.59.0",
 ]
 
+[[package]]
+name = "tokio-cron-scheduler"
+version = "0.14.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "5c71ce8f810abc9fabebccc30302a952f9e89c6cf246fafaf170fef164063141"
+dependencies = [
+ "chrono",
+ "croner",
+ "num-derive",
+ "num-traits",
+ "tokio",
+ "tracing",
+ "uuid",
+]
+
 [[package]]
 name = "tokio-macros"
 version = "2.5.0"
@@ -3926,6 +3961,7 @@ dependencies = [
  "sha2",
  "thiserror",
  "tokio",
+ "tokio-cron-scheduler",
  "tokio-stream",
  "tower",
  "tower-http",