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

15_cloud/summary.md

@@ -1,4 +1,4 @@
-## 本章小结
+## 15.5 本章小结
 
 本章介绍了公有云服务对 Docker 的积极支持，以及新出现的容器云平台。