Add CI build

.github/workflows/build.yml

@@ -0,0 +1,27 @@
+name: build
+on:
+  release:
+    types: [created]
+  push:
+    branches:
+      - '**'
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    permissions:
+      contents: read
+      packages: write
+    steps:
+      - uses: actions/checkout@v4
+      - uses: actions/setup-node@v4
+        with:
+          node-version: '20.x'
+          registry-url: 'https://registry.npmjs.org'
+      - run: npm ci
+      - run: npm run build
+      - run: npm publish
+        # For now we only publish on tags here and assume the version number is already correct.
+        # If we change this then we need to automate updating the version number.
+        if: github.event_name == 'release' && github.event.action == 'created'
+        env:
+          NODE_AUTH_TOKEN: ${{ secrets.NPM_TOKEN }}

.npmrc

@@ -0,0 +1 @@
+access=public