接入原生壳文本文件导入能力

新增 file.importText HostBridge 契约和 H5 facade

移动端通过 Expo DocumentPicker 读取受控文本文件

桌面端通过 Tauri 文件选择框读取受控文本文件

更新壳能力检查、测试、方案文档和共享决策记录

packages/shared/src/contracts/hostBridge.test.ts

@@ -57,6 +57,7 @@ describe('HostBridge shared contract helpers', () => {
     expect(isHostBridgeCapability('network.status')).toBe(true);
     expect(isHostBridgeCapability('network.statusChanged')).toBe(true);
     expect(isHostBridgeCapability('clipboard.readText')).toBe(true);
+    expect(isHostBridgeCapability('file.importText')).toBe(true);
     expect(isHostBridgeCapability('file.importImage')).toBe(true);
     expect(isHostBridgeCapability('file.imageDropped')).toBe(true);
     expect(isHostBridgeCapability('app.setBadgeCount')).toBe(true);

packages/shared/src/contracts/hostBridge.ts

@@ -28,6 +28,7 @@ export const HOST_BRIDGE_METHODS = [
   'clipboard.writeText',
   'clipboard.readText',
   'file.exportText',
+  'file.importText',
   'file.exportImage',
   'file.importImage',
   'haptics.impact',
@@ -291,6 +292,20 @@ export type FileExportTextResult = {
   bytes: number;
 };
 
+export type HostBridgeTextMimeType =
+  | 'text/plain'
+  | 'text/markdown'
+  | 'text/csv'
+  | 'application/json';
+
+export type FileImportTextResult = {
+  action: 'selected';
+  fileName: string;
+  content: string;
+  mimeType: HostBridgeTextMimeType;
+  bytes: number;
+};
+
 export type FileExportImagePayload = {
   fileName: string;
   base64Data: string;