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/docs/zh/ocr-accuracy.md

@@ -76,4 +76,6 @@ TexPixel 在数学公式识别方面达到行业领先的准确率——但准
 
 ---
 
+**延伸阅读：** [提高手写公式识别准确率的 5 个技巧 →](/blog/handwriting-tips)
+
 [上传公式测试识别准确率 →](/app)