Add reusable HTML template export

- Add template export utilities for standard JSON packages and standalone HTML template packages.

- Make the top-level JSON export use the standard surclaw template package format so it can be imported again.

- Add an HTML template package export that embeds A4/print styling and template metadata for visual preview and round-trip import.

- Extend template import to accept both JSON and HTML template package files while keeping old raw template JSON compatible.

- Add tests for package creation, HTML round-trip import, legacy JSON import, and file name cleanup.

- Update template management, feature, progress, testing, and AGENTS documentation for the new export formats.

docs/testing.md

@@ -83,6 +83,7 @@ AI 第三方接口、讯飞语音上游 WebSocket、麦克风权限和真实视
 | 默认字段和 AI Provider | 已覆盖 | `defaultContent.test.ts` |
 | 打印导出入口 | 已覆盖 | `print.test.ts` |
 | 模板列表合并工具 | 已覆盖 | `templateList.test.ts`，防止新增模板被旧本地缓存覆盖。 |
+| 模板导入导出工具 | 已覆盖 | `templateExport.test.ts`，覆盖 JSON/HTML 模板包、HTML 回导、旧 JSON 兼容和文件名清理。 |
 | 默认快捷登录 | 已覆盖 | `e2e/login.spec.ts` |
 | 报告权限 E2E | 已覆盖 | `e2e/report-permissions.spec.ts` |
 | 报告修订版本 E2E | 已覆盖 | `e2e/report-revision.spec.ts` |