style(docs): standardize heading formats and numbering

- Enforce Level 1-3 structural numbering based on SUMMARY.md hierarchy
- Remove structural numbering from Level 4+ headings
- Eliminate single child headings by converting to bold text
- Auto-inject summary text for headings with multiple children missing intro text
- Exclude Appendix chapters from structural numbering
- Avoid modifying code block contents
- Add script to detect non-standard English usage in headers

19_cases/ci/actions/README.md

@@ -23,10 +23,10 @@ jobs:
           args: go version
 ```
 
-## 概述
+## 19.9 概述
 
 总体概述了以下内容。
 
-## 参考资料
+## 19.9 参考资料
 
 * [Actions Docs](https://docs.github.com/en/actions)