ci: add GitHub Actions workflows for deployment

- Add deploy.yml for automatic deployment on main push
- Add test-deploy.yml for PR build verification
- Support manual trigger via workflow_dispatch
- Use peaceiris/actions-gh-pages for gh-pages branch deployment

Author: yhk1038

.github/workflows/deploy.yml

@@ -0,0 +1,51 @@
+name: Deploy to GitHub Pages
+
+on:
+  push:
+    branches:
+      - main
+  workflow_dispatch:
+
+permissions:
+  contents: write
+
+concurrency:
+  group: pages-deploy-${{ github.ref }}
+  cancel-in-progress: true
+
+jobs:
+  deploy:
+    name: Build and Deploy
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+        with:
+          fetch-depth: 0
+
+      - name: Setup pnpm
+        uses: pnpm/action-setup@v4
+        with:
+          version: 9
+
+      - name: Setup Node.js
+        uses: actions/setup-node@v4
+        with:
+          node-version: 20
+          cache: pnpm
+
+      - name: Install dependencies
+        run: pnpm install --frozen-lockfile
+
+      - name: Build website
+        run: pnpm run build
+        env:
+          NODE_OPTIONS: --max-old-space-size=8192
+
+      - name: Deploy to GitHub Pages
+        uses: peaceiris/actions-gh-pages@v4
+        with:
+          github_token: ${{ secrets.GITHUB_TOKEN }}
+          publish_dir: ./build
+          user_name: github-actions[bot]
+          user_email: github-actions[bot]@users.noreply.github.com

.github/workflows/test-deploy.yml

@@ -0,0 +1,39 @@
+name: Test Deployment Build
+
+on:
+  pull_request:
+    branches:
+      - main
+
+concurrency:
+  group: test-deploy-${{ github.ref }}
+  cancel-in-progress: true
+
+jobs:
+  test-deploy:
+    name: Test Build
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+        with:
+          fetch-depth: 0
+
+      - name: Setup pnpm
+        uses: pnpm/action-setup@v4
+        with:
+          version: 9
+
+      - name: Setup Node.js
+        uses: actions/setup-node@v4
+        with:
+          node-version: 20
+          cache: pnpm
+
+      - name: Install dependencies
+        run: pnpm install --frozen-lockfile
+
+      - name: Test build
+        run: pnpm run build
+        env:
+          NODE_OPTIONS: --max-old-space-size=8192