feat: add GitHub Pages deployment workflow for demo site

- Added GitHub Actions workflow to automatically deploy demo site to GitHub Pages
- Configured Next.js for static export with proper base path and asset prefix for GitHub Pages
- Added new build:gh script to generate GitHub Pages-compatible build
- Set up concurrency controls to prevent parallel deployments
- Configured necessary GitHub permissions for Pages deployment

Author: Erics1337

.github/workflows/deploy-demo.yml

@@ -0,0 +1,49 @@
+name: Deploy Demo (Next.js static export) 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 Node
+        uses: actions/setup-node@v4
+        with:
+          node-version: 20
+          cache: 'npm'
+
+      - name: Install dependencies
+        run: npm ci
+
+      - name: Build demo for GitHub Pages
+        run: npm run build:gh --workspace=@crest-ui/demo
+
+      - name: Upload static site
+        uses: actions/upload-pages-artifact@v3
+        with:
+          path: apps/demo/out
+
+  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

apps/demo/next.config.mjs

@@ -1,6 +1,16 @@
 /** @type {import('next').NextConfig} */
+const isGhPages = process.env.GITHUB_PAGES === 'true';
+
 const nextConfig = {
   transpilePackages: ["@crest-ui/ui", "@crest-ui/config", "@crest-ui/tokens"],
+  output: 'export',
+  trailingSlash: true,
+  ...(isGhPages
+    ? {
+        basePath: '/crest-ui',
+        assetPrefix: '/crest-ui/',
+      }
+    : {})
 };
 
-export default nextConfig;
+export default nextConfig;

apps/demo/package.json

@@ -5,6 +5,7 @@
   "scripts": {
     "dev": "next dev -p 3000",
     "build": "next build",
+    "build:gh": "GITHUB_PAGES=true next build",
     "start": "next start -p 3000",
     "lint": "next lint"
   },