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

@@ -68,4 +68,6 @@ $$A = U \Sigma V^T$$
 
 一个学期下来，你会积累几十个识别出的公式。不妨整理一下：将每个公式粘贴到一个参考 `.tex` 文件中，加上简短注释。期末时，你将拥有一份几乎不费力气就建立起来的、可搜索的个人公式表。
 
+**参考文档：** 关于支持的文件类型、大小限制和复制选项，请查看 [图片转 LaTeX 文档 →](/docs/image-to-latex)
+
 [开始数字化你的笔记 →](/app)