ci: auto-deploy Skill Playground to GitHub Pages

On push to main, rebuild web/skills.json from the SKILL.md files and publish
web/ to GitHub Pages, so the live site always reflects the current skill
library. Manual runs supported via workflow_dispatch.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

.github/workflows/deploy-playground.yml

@@ -0,0 +1,58 @@
+name: Deploy Skill Playground
+
+# Rebuilds web/skills.json from the SKILL.md files and publishes web/ to
+# GitHub Pages. Runs on every push to main that touches skills or the web app,
+# so the live site always reflects the current skill library.
+
+on:
+  push:
+    branches: [main]
+    paths:
+      - 'skills/**'
+      - 'web/**'
+      - '.github/workflows/deploy-playground.yml'
+  workflow_dispatch:
+
+permissions:
+  contents: read
+  pages: write
+  id-token: write
+
+# Allow one concurrent deployment; cancel in-progress runs for the same ref.
+concurrency:
+  group: pages
+  cancel-in-progress: true
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+
+      - name: Set up Node
+        uses: actions/setup-node@v4
+        with:
+          node-version: '20'
+
+      - name: Rebuild skills.json from SKILL.md files
+        run: node web/build-skills.mjs
+
+      - name: Configure Pages
+        uses: actions/configure-pages@v5
+
+      - name: Upload web/ as Pages artifact
+        uses: actions/upload-pages-artifact@v3
+        with:
+          path: web
+
+  deploy:
+    needs: build
+    runs-on: ubuntu-latest
+    environment:
+      name: github-pages
+      url: ${{ steps.deployment.outputs.page_url }}
+    steps:
+      - name: Deploy to GitHub Pages
+        id: deployment
+        uses: actions/deploy-pages@v4