ci: add GitHub Actions workflow to deploy web pages to GitHub Pages

Builds Re:VIEW web output and search index on push to main,
then deploys to GitHub Pages via actions/deploy-pages.
Requires Pages source set to 'GitHub Actions' in repo settings.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: piti6

.github/workflows/deploy-web.yml

@@ -0,0 +1,65 @@
+name: Deploy Web to GitHub Pages
+
+on:
+  push:
+    branches: [main]
+  workflow_dispatch:
+
+permissions:
+  contents: read
+  pages: write
+  id-token: write
+
+concurrency:
+  group: pages
+  cancel-in-progress: true
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+
+      - name: Setup Ruby
+        uses: ruby/setup-ruby@v1
+        with:
+          ruby-version: '3.3'
+          bundler-cache: true
+
+      - name: Setup Node.js
+        uses: actions/setup-node@v4
+        with:
+          node-version: '20'
+          cache: 'npm'
+
+      - name: Install npm dependencies
+        run: npm install --ignore-scripts
+
+      - name: Install gem dependencies
+        run: bundle install
+
+      - name: Build web pages
+        run: REVIEW_CONFIG_FILE=config-epub-jp.yml npx grunt web
+
+      - name: Build search index
+        run: node build-search-index.js
+
+      - name: Setup Pages
+        uses: actions/configure-pages@v4
+
+      - name: Upload artifact
+        uses: actions/upload-pages-artifact@v3
+        with:
+          path: articles/webroot
+
+  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