ci(ci): add GitHub Actions workflow for documentation site deployment

.github/workflows/docs.yml

@@ -0,0 +1,80 @@
+name: Docs
+
+on:
+  push:
+    branches: [main]
+    paths:
+      - "docs/**"
+      - "blume.config.ts"
+      - "package.json"
+      - "package-lock.json"
+      - ".github/workflows/docs.yml"
+  pull_request:
+    paths:
+      - "docs/**"
+      - "blume.config.ts"
+      - "package.json"
+      - "package-lock.json"
+      - ".github/workflows/docs.yml"
+  workflow_dispatch:
+
+# GITHUB_TOKEN permissions for Pages deployment via OIDC.
+permissions:
+  contents: read
+  pages: write
+  id-token: write
+
+# Serialize deployments; never cancel a running one mid-publish.
+concurrency:
+  group: pages
+  cancel-in-progress: false
+
+jobs:
+  build:
+    name: Build site
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+        with:
+          # Full history so Blume's `lastModified` can read per-page commit dates.
+          fetch-depth: 0
+
+      - name: Setup Node
+        uses: actions/setup-node@v4
+        with:
+          # Blume requires Node 22.12 or newer.
+          node-version: "22.x"
+          cache: npm
+
+      - name: Install dependencies
+        run: npm ci
+
+      - name: Configure Pages
+        id: pages
+        uses: actions/configure-pages@v5
+
+      - name: Build
+        run: npm run build
+        env:
+          # Lifts the GitHub API rate limit for build-time repo metadata.
+          GITHUB_TOKEN: ${{ github.token }}
+
+      - name: Upload artifact
+        uses: actions/upload-pages-artifact@v3
+        with:
+          path: dist
+
+  deploy:
+    name: Deploy to Pages
+    # Deploy only from main; pull requests build as a check and stop there.
+    if: github.event_name != 'pull_request'
+    needs: build
+    runs-on: ubuntu-latest
+    environment:
+      name: github-pages
+      url: ${{ steps.deployment.outputs.page_url }}
+    steps:
+      - name: Deploy
+        id: deployment
+        uses: actions/deploy-pages@v4