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/en/2026-02-01-student-workflow.md

@@ -68,4 +68,6 @@ With TexPixel: photograph it, get `A = U \Sigma V^T` in one second, paste. For m
 
 Over a semester, you'll accumulate dozens of recognized formulas. Consider organizing them: paste each into a reference `.tex` file with a short comment. By exam time, you'll have a searchable personal formula sheet that took almost no effort to build.
 
+**See also:** For supported file types, size limits, and copy options, see the [Image to LaTeX documentation →](/docs/image-to-latex)
+
 [Start digitizing your notes →](/app)