feat: add GitHub Actions workflows for build and deploy preview

- Introduced a new workflow for building the preview site and uploading build artifacts.
- Added a deployment workflow to Cloudflare Pages triggered by the successful completion of the build workflow.
- Configured Node.js and pnpm for dependency management and build processes.

.github/workflows/build-preview.yml

@@ -0,0 +1,37 @@
+name: Build Preview Deployment
+
+on:
+  pull_request:
+    types: [opened, synchronize]
+
+jobs:
+  build-preview:
+    runs-on: ubuntu-latest
+    name: Build Preview Site and Upload Build Artifact
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+
+      - name: Setup Node.js
+        uses: actions/setup-node@v4
+        with:
+          node-version: '20'
+
+      - name: Setup pnpm
+        uses: pnpm/action-setup@v2
+        with:
+          version: 8
+
+      - name: Install dependencies
+        working-directory: app
+        run: pnpm install
+
+      - name: Build
+        working-directory: app
+        run: pnpm build
+
+      - name: Upload build artifact
+        uses: actions/upload-artifact@v4
+        with:
+          name: preview-build
+          path: app/dist