ci: add GitHub Actions workflow

Run lint, format check, typecheck, test, and build on push/PR to main.

Author: jonwiggins

.github/workflows/ci.yml

@@ -0,0 +1,36 @@
+name: CI
+
+on:
+  push:
+    branches: [main]
+  pull_request:
+    branches: [main]
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+
+    steps:
+      - uses: actions/checkout@v4
+
+      - uses: actions/setup-node@v4
+        with:
+          node-version: 22
+          cache: npm
+
+      - run: npm ci
+
+      - name: Lint
+        run: npm run lint
+
+      - name: Format check
+        run: npm run format:check
+
+      - name: Typecheck
+        run: tsc -b
+
+      - name: Test
+        run: npm test
+
+      - name: Build
+        run: npm run build