chore: Initialize Astro + Starlight + Tailwind + i18n project scaffold

[100gle]

Parent Issue

Part of #2

Objective

Set up the entire project foundation so subsequent sub-issues can build on a working scaffold.

Tasks

• Run npm create astro@latest -- --template starlight to initialize the project (in website/ dir)
• Install and configure Tailwind CSS (@astrojs/tailwind)
• Configure Starlight i18n in astro.config.mjs:
  • defaultLocale: 'en'
  • locales: { en: { label: 'English' }, 'zh-cn': { label: '简体中文' } }
• Set up base URL and site metadata (site: 'https://bub.build')
• Create src/styles/global.css with Tailwind directives and basic design tokens
• Create placeholder src/content/docs/en/index.mdx and src/content/docs/zh-cn/index.mdx
• Configure sidebar structure in astro.config.mjs (empty groups for: Getting Started, Concepts, Guides, Extending, Reference, Blog)
• Add scripts in package.json: dev, build, preview
• Verify npm run build passes with no errors
• Add .gitignore for node_modules/, dist/, .astro/

Acceptance Criteria

• npm run dev starts successfully
• Both / and /zh-cn/ routes render
• Tailwind classes work in .astro components
• Starlight sidebar shows placeholder structure
• npm run build produces valid static output

Tech Notes

• Astro 5.x + Starlight latest
• Tailwind CSS 4.x via @astrojs/tailwind
• Node.js 20+
• Project location: website/ in repo root

[100gle]

✅ Completed — Astro + Starlight + Tailwind + i18n scaffold is in place under website/. npm run dev, npm run build both work. Both / and /zh-cn/ routes render. Build produces 37 static pages.