add CI workflow

.github/workflows/check.yml

@@ -0,0 +1,22 @@
+name: check
+on:
+  pull_request:
+  push:
+    branches:
+      - main
+
+jobs:
+  check:
+    runs-on: ubuntu-latest
+    steps:
+      # Set up
+      - uses: actions/checkout@v4
+      - uses: actions/setup-node
+        with:
+          node-version: "20" # Oldest LTS at time of writing
+      - run: npm ci
+
+      # Run checks
+      - run: npm run format:check
+      - run: npm run lint:check
+      - run: npm run build