ci: add workflow for building API documentation

Author: yoshoku

.github/workflows/documentation.yml

@@ -0,0 +1,39 @@
+name: documentation
+
+on:
+  workflow_dispatch:
+
+permissions:
+  contents: read
+  pages: write
+  id-token: write
+
+concurrency:
+  group: "pages"
+  cancel-in-progress: false
+
+jobs:
+  deploy:
+    environment:
+      name: github-pages
+      url: ${{ steps.deployment.outputs.page_url }}
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v6
+      - name: Setup Ruby
+        uses: actions/setup-ruby@v1
+        with:
+          ruby-version: 3.4
+          bundler-cache: true
+      - name: Build API documentation
+        run: bundle exec yard doc -o output/doc
+      - name: Upload API documentation
+        uses: actions/upload-pages-artifact@v4
+        with:
+          path: output
+      - name: Setup Pages
+        uses: actions/configure-pages@v5
+      - name: Deploy to GitHub Pages
+        id: deployment
+        uses: actions/deploy-pages@v4