MkDocs Site PRD Summary

The documentation site must be implemented as an independent MkDocs project under docs-site/.

Key requirements:

• Use MkDocs as the documentation framework.
• Use an i18n plugin for bilingual documentation.
• Keep Chinese content under docs-site/docs/zh/.
• Keep English content under docs-site/docs/en/.
• Create both language trees from the first implementation.
• Keep navigation structure consistent between Chinese and English.
• Support GitHub Actions build and GitHub Pages deployment.

The full source PRD is maintained at docs-site/mkdocs_prd.md.