接入桌面壳文本文件导出能力

新增 HostBridge file.exportText 契约、文件名清洗和 H5 导出入口

Tauri 桌面壳通过受控 host_bridge_request 打开保存对话框并写入文本文件

Expo 移动壳对未接入的文件导出能力明确返回 unsupported

更新宿主壳方案、统一协议和项目共享决策记录

apps/desktop-shell/scripts/check-config.mjs

@@ -34,7 +34,7 @@ const requiredUrlParts = [
   'hostShell=tauri_desktop',
   'hostPlatform=unknown',
   'bridgeVersion=1',
-  'hostCapabilities=host.getRuntime,share.open,share.setTarget,app.openExternalUrl,app.setTitle,clipboard.writeText',
+  'hostCapabilities=host.getRuntime,share.open,share.setTarget,app.openExternalUrl,app.setTitle,clipboard.writeText,file.exportText',
 ];
 
 for (const part of requiredUrlParts) {
@@ -57,7 +57,10 @@ const requiredMainSnippets = [
   '"share.setTarget"',
   '"app.setTitle"',
   '"clipboard.writeText"',
+  '"file.exportText"',
+  'tauri_plugin_dialog::init()',
   '"copied_to_clipboard"',
+  '"file export cancelled"',
   'set_title',
 ];