新增: 模板系统+工作流节点(YAML加载器+GitNode/HTTPNode/NotifyNode)

- template_loader.rs: YAML→DagDef加载器+校验(空节点/未知类型/依赖环/边引用)

- GitNode: 分支/checkout/commit/merge/push/status/log(git CLI封装)

- HTTPNode: GET/POST/PUT/DELETE(reqwest,30s超时)

- NotifyNode: 桌面通知(日志)+ Webhook(飞书/钉钉/自定义)

- 8个模板加载器测试+37个节点测试全绿

crates/df-nodes/Cargo.toml

@@ -15,3 +15,4 @@ tokio = { workspace = true }
 async-trait = { workspace = true }
 anyhow = { workspace = true }
 tracing = { workspace = true }
+reqwest = { version = "0.12", default-features = false, features = ["json", "rustls-tls"] }