阶段1-rpa-core建包: engine+31个纯Node能力迁入packages/rpa-core, 领域类型单一源化, createEngine工厂收拢模块级状态

- engine/(registry/types/runtime/expression)物理迁入包, 解耦shared/types(域类型归包, 宿主type-only re-export)
- 31个纯Node能力+27个测试迁入包; 宿主留守Electron/浏览器/AI依赖能力, index.ts经@rpa/core/capabilities拉起
- 新增createEngine()/defaultEngine: excel缓存/Excel句柄/db连接/FTP客户端/OCR实例/拟真设置挂引擎实例
- remaining-core子流程依赖改为host-bridge注入, 包内不再import宿主flows
- 宿主main/index.ts启动时注入子流程源; electron-vite/vitest/tsconfig配@rpa/core源码别名
- 验证: typecheck绿, 快照909个id diff为零, 332测试过(2个桌面冒烟因会话无交互SetForegroundWindow被拒, 环境阻塞)

packages/rpa-core/src/engine/host-bridge.ts

@@ -0,0 +1,22 @@
+import type { FlowDefinition } from "../types";
+
+/**
+ * 宿主桥（HostBridge 候选，阶段 2 正式化接口）。
+ *
+ * 包内个别能力需要宿主数据（目前仅子流程仓库），通过显式 setter 注入，
+ * 包本身不得 import 宿主模块。宿主启动时调用 setSubflowSource()。
+ */
+export interface SubflowSource {
+  listFlows(): Promise<Array<{ id: string; name: string }>>;
+  getFlow(id: string): Promise<FlowDefinition>;
+}
+
+let subflowSource: SubflowSource | undefined;
+
+export function setSubflowSource(source: SubflowSource): void {
+  subflowSource = source;
+}
+
+export function getSubflowSource(): SubflowSource | undefined {
+  return subflowSource;
+}