修复: Wave5 审批子系统收尾（R7补 types.ts + R9⑪ failed_node + R8 Request 测试）

- R7补: types.ts event.type string→WorkflowEventType 字面量联合(11 变体 snake_case)，静态拦截写错 type
- R9⑪: workflow.rs WorkflowFailed failed_node String::new()→状态机取首个 Failed/Cancelled 节点
- R8: human_node 加 request_is_emitted_to_bus 测试，验证 R6(Request 真发到 EventBus)
cargo/vue-tsc 0 err / df-nodes 15 test pass

src/api/types.ts

@@ -121,10 +121,16 @@ export interface WorkflowRecord {
 }
 
 /** 工作流事件载荷（后端 emit 的结构） */
+/** 工作流事件类型字面量联合(对应后端 WorkflowEvent serde tag=type rename_all=snake_case，R7收窄防写错 type 字符串) */
+export type WorkflowEventType =
+  | 'node_started' | 'node_progress' | 'node_output' | 'node_completed' | 'node_failed'
+  | 'workflow_paused' | 'workflow_completed' | 'workflow_failed'
+  | 'human_approval_request' | 'human_approval_response'
+
 export interface WorkflowEventPayload {
   execution_id: string
   event: {
-    type: string
+    type: WorkflowEventType
     [key: string]: unknown
   }
 }