ci: add GitHub Pages deploy workflow for docs

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

Author: ryo-manba

.github/workflows/deploy-docs.yml

@@ -0,0 +1,41 @@
+name: Deploy Docs
+
+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:
+      - uses: actions/checkout@v4
+      - uses: pnpm/action-setup@v4
+      - uses: actions/setup-node@v4
+        with:
+          node-version: 24
+          cache: pnpm
+      - run: pnpm install
+      - run: pnpm docs:build
+      - uses: actions/upload-pages-artifact@v3
+        with:
+          path: docs/dist
+
+  deploy:
+    needs: build
+    runs-on: ubuntu-latest
+    environment:
+      name: github-pages
+      url: ${{ steps.deployment.outputs.page_url }}
+    steps:
+      - id: deployment
+        uses: actions/deploy-pages@v4