Add Astro project site with readable, searchable book, blog, and history

- site/: Astro 7 project — homepage, MDX blog, history page, and the full
  book rendered one page per section from the AsciiDoc sources via
  Asciidoctor.js (same splitting strategy as builder/src/site.rs)
- Full-text search over book and blog with Pagefind
- .github/workflows/deploy-site.yml: build on push to main and publish
  site/dist to the gh-pages branch

Co-authored-by: Scott Chacon <schacon@gmail.com>

Author: cursoragent

.github/workflows/deploy-site.yml

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+name: Deploy site to GitHub Pages
+
+on:
+  push:
+    branches: [ main ]
+  workflow_dispatch:
+
+permissions:
+  contents: write
+
+concurrency:
+  group: deploy-site
+  cancel-in-progress: true
+
+jobs:
+  deploy:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v7
+        with:
+          # Full history so the build can derive the revision number from tags
+          # and the contributors list from the shortlog.
+          fetch-depth: 0
+
+      - name: Set up Node
+        uses: actions/setup-node@v4
+        with:
+          node-version: 22
+          cache: npm
+          cache-dependency-path: site/package-lock.json
+
+      - name: Install dependencies
+        working-directory: site
+        run: npm ci
+
+      - name: Build site
+        working-directory: site
+        run: npm run build
+
+      - name: Publish to gh-pages
+        uses: peaceiris/actions-gh-pages@v4
+        with:
+          github_token: ${{ secrets.GITHUB_TOKEN }}
+          publish_branch: gh-pages
+          publish_dir: site/dist
+          force_orphan: true

site/.gitignore

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+# dependencies
+node_modules/
+
+# build output
+dist/
+.astro/
+
+# generated by scripts/build-book.mjs
+src/generated/
+public/images/
+public/book-cover.png
+public/favicon.ico

site/README.md

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+# Pro Git project site
+
+The source for the project website, built with [Astro](https://astro.build). It has:
+
+- a **homepage** introducing the book,
+- the **full book, readable online** — one page per section, rendered from the
+  AsciiDoc sources in this repository with
+  [Asciidoctor.js](https://github.com/asciidoctor/asciidoctor.js),
+- **full-text search** over the book and blog, powered by
+  [Pagefind](https://pagefind.app),
+- a **blog** (MDX, in `src/content/blog/`) for updates and progress on the
+  third edition,
+- a **history of the book** page.
+
+## How the book gets onto the site
+
+`scripts/build-book.mjs` runs before every dev/build. It converts `../progit.asc`
+(including all chapter includes) to HTML, splits the result into one page per
+section — the same strategy as `builder/src/site.rs` — rewrites cross-references
+and image paths, and writes:
+
+- `src/generated/book.json` — consumed by `src/pages/book/[slug].astro`,
+- `public/images/`, `public/book-cover.png`, `public/favicon.ico` — copied from
+  the repository.
+
+All of those outputs are git-ignored; the book is never duplicated in the repo.
+
+## Commands
+
+Run these from the `site/` directory:
+
+| Command           | Action                                                       |
+| ----------------- | ------------------------------------------------------------ |
+| `npm install`     | Install dependencies                                         |
+| `npm run dev`     | Regenerate the book, then start the dev server               |
+| `npm run build`   | Regenerate the book, build to `dist/`, index it with Pagefind |
+| `npm run preview` | Serve the built `dist/` locally                              |
+
+Note: search only works on the *built* site (`npm run build` + `npm run preview`),
+because Pagefind indexes the generated HTML.
+
+## Writing a blog post
+
+Add an `.mdx` file to `src/content/blog/` with this frontmatter:
+
+```mdx
+---
+title: 'Post title'
+description: 'One-sentence summary shown in lists and search results.'
+date: 2026-08-02
+author: 'Your Name'   # optional
+---
+
+Post body in MDX…
+```
+
+The file name (without `.mdx`) becomes the URL: `/blog/<file-name>/`.
+
+## Deployment
+
+`.github/workflows/deploy-site.yml` builds the site on every push to `main` and
+publishes `site/dist/` to the `gh-pages` branch with
+[peaceiris/actions-gh-pages](https://github.com/peaceiris/actions-gh-pages).
+Point GitHub Pages at the `gh-pages` branch (Settings → Pages → Deploy from a
+branch) and the site is served at <https://progit.github.io/progit3/>.
+
+The canonical URL and base path default to `https://progit.github.io` and
+`/progit3`; override them with the `SITE_URL` and `BASE_PATH` environment
+variables (e.g. for a fork or a custom domain).

site/astro.config.mjs

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+// @ts-check
+import { defineConfig } from 'astro/config';
+import mdx from '@astrojs/mdx';
+
+// GitHub Pages project site: https://progit.github.io/progit3/
+// Override SITE_URL / BASE_PATH for forks or a custom domain.
+const site = process.env.SITE_URL ?? 'https://progit.github.io';
+const base = process.env.BASE_PATH ?? '/progit3';
+
+export default defineConfig({
+  site,
+  base,
+  trailingSlash: 'ignore',
+  integrations: [mdx()],
+  build: {
+    format: 'directory',
+  },
+});