refactor: port site from Jekyll to Astro

CLAUDE.md

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+# CLAUDE.md
+
+This file provides guidance to Claude Code (claude.ai/code) when working with
+code in this repository.
+
+## Project Overview
+
+This is the source for commonflow.org, an Astro-based static site that documents
+the Git Common-Flow specification. Common-Flow is a git workflow specification
+that combines GitHub Flow with versioned releases.
+
+## Build Commands
+
+```bash
+# Install dependencies
+npm install
+
+# Development server
+npm run dev
+
+# Build site (outputs to docs/ directory)
+npm run build
+
+# Preview built site
+npm run preview
+
+# Update specs from upstream (fetches from github.com/jimeh/common-flow)
+npm run update
+```
+
+The site is built to `docs/` for GitHub Pages hosting.
+
+## Architecture
+
+- **Astro 5.x** static site generator
+- **Tailwind CSS 4.x** for styling with dark mode support
+- **Content Collections** for spec markdown files
+- **TypeScript** throughout
+
+### Key Files
+
+- `src/config.ts` - Site configuration with version list
+- `src/content.config.ts` - Astro content collection definition
+- `src/layouts/Default.astro` - Main layout with sidebar
+- `src/components/` - Sidebar, MenuToggle, ThemeToggle components
+- `src/pages/spec/[version].astro` - Dynamic route for spec versions
+- `src/content/spec/*.md` - Versioned spec documents
+- `public/spec/*.svg` - SVG diagrams for each version
+- `scripts/update-specs.ts` - Fetches specs from GitHub
+
+### Updating Spec Versions
+
+1. Add new version to `versions` array in `src/config.ts`
+2. Update `currentVersion` if this is the new default
+3. Run `npm run update` to fetch specs from GitHub
+4. Run `npm run build` to rebuild the site