feat: add bilingual project website and GitHub Pages deployment

[chlins]

Summary

• Add a responsive bilingual modctl website and Markdown getting-started guide using Hugo 0.167.0 native multilingual support.
• Keep translated content in content/en and content/zh, UI messages in i18n/*.json, and page structure in shared Hugo layouts.
• Generate independent English and Chinese URLs, canonical/hreflang metadata, translated SVG labels, and sitemaps at build time.
• Remove the prototype data-zh DOM replacement, client-side language branches, and custom Node build/server code. JavaScript only enhances copy controls, navigation, tabs, and table of contents.
• Preserve the custom visual design. Go application code is unchanged.
• GitHub Pages CI installs a pinned, checksum-verified Hugo binary. PRs test/build only, upstream main deploys with job-scoped permissions.

Validation

• 10 tests passed, using actual Hugo builds: locale/content completeness, frontmatter parity, Pages subpath links/anchors, reciprocal language metadata, copy render hooks, complete no-JS workflow content, and SVG special-character/injection escaping.
• Strict production build passes with --printI18nWarnings --panicOnWarning.
• Missing-translation and missing-content mutations were verified to fail rather than silently fall back.
• Browser checks pass for four page/locale routes across seven viewport sizes (28 combinations), language link navigation, copy, keyboard tabs, mobile menu, and no-JavaScript Chinese content.
• axe-core WCAG A/AA checks found no violations on both pages in both languages.

Language URLs

• English: https://modelpack.github.io/modctl/
• Chinese: https://modelpack.github.io/modctl/zh/
• Documentation: getting-started/ under each locale.

Language is determined by URL, not browser storage or a runtime DOM translation script. The previous prototype ?lang=zh parameter is replaced by /zh/.

Deployment

GitHub Pages is configured with GitHub Actions as its source, HTTPS enforced, and the github-pages environment restricted to main.

"All changes are squashed into one signed-off commit, and the DCO check passes. This PR still needs the required two approvals." After merge, the Website workflow will publish automatically. No custom domain, additional token, or gh-pages branch is needed. The public site is not deployed yet.

[gaius-qi]

LGTM