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/20.4_terminology.md

@@ -1,4 +1,4 @@
-## 16.4 术语词表 (出版统一版)
+## 术语词表 (出版统一版)
 
 本词表用于统一全书术语、缩写和命令表达，适用于最终出版前清稿。