Add GitHub Actions build check for pull requests (#62)

Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: tim-webflow

.github/workflows/build.yml

@@ -0,0 +1,24 @@
+name: Build
+
+on:
+  pull_request:
+    branches:
+      - main
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Set up Node.js
+        uses: actions/setup-node@v4
+        with:
+          node-version: 20
+          cache: npm
+
+      - name: Install dependencies
+        run: npm ci
+
+      - name: Build
+        run: npm run build