refact: eliminate blog/docs content overlap

- Delete blog/copy-math-to-word (EN+ZH) — identical to docs/copy-to-word
- Rewrite blog/pdf-formula-issues as narrative troubleshooting story;
  operational steps now link out to docs/pdf-extraction
- Add "Further reading" cross-links: 4 docs → relevant blog posts
- Add "See also" cross-links: 3 blog posts → relevant docs

Docs = product reference; Blog = narrative/use cases/opinions

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

content/blog/zh/2026-03-20-handwriting-tips.md

@@ -43,3 +43,5 @@ TexPixel 在每张图片只包含一个公式或一组紧密相关的表达式
 ---
 
 养成这些习惯后，你会发现识别准确率明显提升——即使是复杂的手写表达式也能达到 95% 以上。
+
+**参考文档：** 关于影响准确率的系统性分析（分辨率、对比度、公式复杂度），请查看 [识别准确率文档 →](/docs/ocr-accuracy)