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/en/ocr-accuracy.md

@@ -76,4 +76,6 @@ Contact us at: [support@texpixel.com](mailto:support@texpixel.com)
 
 ---
 
+**Further reading:** [5 Tips for Better Handwriting Recognition →](/blog/handwriting-tips)
+
 [Upload a formula and test accuracy →](/app)