docs: user documentation site on GitHub Pages (family rollout)

[shigechika]

Summary

Roll out the family documentation-site pattern to this repository: a task-oriented user guide on GitHub Pages, complementing the reference README.

Template (live example): https://github.com/shigechika/mcp-stdio — issue shigechika/mcp-stdio#284, scaffold PR shigechika/mcp-stdio#285, published at https://shigechika.github.io/mcp-stdio/ (Japanese at /ja/).

Steps

1. Copy the three-piece scaffold from mcp-stdio and adapt:
   • mkdocs.yml — change site_name / site_url / repo_url / nav; MkDocs Material + mkdocs-static-i18n (suffix layout, *.ja.md). Drop the i18n plugin if this repo is English-only.
   • docs/ — Home (what it is + quickstart) and task-oriented guides for this tool's main workflows.
   • .github/workflows/docs.yml — mkdocs build --strict on docs PRs; deploy via upload-pages-artifact + deploy-pages on push to main. Pin mkdocs-material>=9.7,<10 (MkDocs 2.0 is currently unlicensed per the mkdocs-material 2026-02-18 advisory).
2. Repo settings → Pages → Source: GitHub Actions.
3. Add site/ to .gitignore; link the site from README (and README.ja.md if present).

docs: commits stay invisible to release-please where it is used.