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

appendix/20.1_best_practices.md

@@ -1,4 +1,4 @@
-## 16.1 Dockerfile 最佳实践
+## Dockerfile 最佳实践
 
 本附录是笔者对 Docker 官方文档中 [Best practices for writing Dockerfiles](https://docs.docker.com/develop/develop-images/dockerfile_best-practices/) 的理解与翻译。