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/20.3_resources.md

@@ -1,4 +1,4 @@
-## 16.3 资源链接
+## 资源链接
 
 本节涵盖了相关内容与详细描述，主要探讨以下几个方面：