feat: add AI-generated teaser system with revision tracking

Add infrastructure for automatically generating Open Graph teasers
using the Anthropic API, with content-hash-based revision tracking
to avoid unnecessary regeneration. Teasers are word-wrapped at 90
characters to respect the project's 92-char line width in YAML
frontmatter. The CD workflow calls update-revisions and
generate-teasers as separate steps and commits any changes.

Author: limulus

.github/workflows/cd.yaml

@@ -38,6 +38,8 @@ jobs:
   build:
     runs-on: ubuntu-latest
     name: build website
+    permissions:
+      contents: write
     steps:
       - uses: actions/checkout@v5
       - uses: actions/setup-node@v6
@@ -48,6 +50,10 @@ jobs:
       - run: npm ci
         env:
           NODE_AUTH_TOKEN: ${{ secrets.NPM_TOKEN }}
+      - run: npm run update-revisions
+      - run: npm run generate-teasers
+        env:
+          ANTHROPIC_API_KEY: ${{ secrets.ANTHROPIC_API_KEY }}
       - run: npm run build
         env:
           MAPBOX_PUBLIC_TOKEN: ${{ secrets.MAPBOX_PUBLIC_TOKEN }}
@@ -56,6 +62,13 @@ jobs:
           name: dist-www
           path: dist/www
           retention-days: 15
+      - name: Commit auto-generated teasers
+        run: |
+          git config user.name "github-actions[bot]"
+          git config user.email "github-actions[bot]@users.noreply.github.com"
+          git add "www/**/*.md" .revisions.json
+          git diff --cached --quiet || \
+            git commit -m "chore: auto-generate teasers [skip ci]" && git push
 
   deploy:
     needs: