Add GitHub Pages deployment workflow

- Add GitHub Actions workflow for building and deploying to Pages
- Configure Astro site/base for GitHub Pages subdirectory
- Copy scaffold.py to public/ for download serving
- Update scaffold download URL in docs

Site will deploy to: https://waveform-analytics.github.io/spec-driven-site/

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: michellejw

.github/workflows/deploy.yml

@@ -0,0 +1,53 @@
+name: Deploy to GitHub Pages
+
+on:
+  push:
+    branches: [main]
+  workflow_dispatch:
+
+permissions:
+  contents: read
+  pages: write
+  id-token: write
+
+concurrency:
+  group: "pages"
+  cancel-in-progress: false
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+
+      - name: Setup Node
+        uses: actions/setup-node@v4
+        with:
+          node-version: 20
+          cache: npm
+
+      - name: Setup Pages
+        uses: actions/configure-pages@v4
+
+      - name: Install dependencies
+        run: npm ci
+
+      - name: Build Astro site
+        run: npm run build
+
+      - name: Upload artifact
+        uses: actions/upload-pages-artifact@v3
+        with:
+          path: ./dist
+
+  deploy:
+    environment:
+      name: github-pages
+      url: ${{ steps.deployment.outputs.page_url }}
+    runs-on: ubuntu-latest
+    needs: build
+    steps:
+      - name: Deploy to GitHub Pages
+        id: deployment
+        uses: actions/deploy-pages@v4

astro.config.mjs

@@ -4,6 +4,8 @@ import starlight from '@astrojs/starlight';
 
 // https://astro.build/config
 export default defineConfig({
+	site: 'https://waveform-analytics.github.io',
+	base: '/spec-driven-site',
 	integrations: [
 		starlight({
 			title: 'Spec-Driven Science',