Add initial CI workflow

.github/workflows/ci.yml

@@ -0,0 +1,47 @@
+name: CI
+
+on:
+  pull_request:
+  push:
+    branches:
+      - main
+
+permissions:
+  contents: read
+
+jobs:
+  checks:
+    name: Quality checks
+    runs-on: ubuntu-latest
+
+    steps:
+      - name: Check out repository
+        uses: actions/checkout@v6
+
+      - name: Set up pnpm
+        uses: pnpm/action-setup@v6
+
+      - name: Set up Node.js
+        uses: actions/setup-node@v6
+        with:
+          node-version: 22
+          cache: pnpm
+          cache-dependency-path: pnpm-lock.yaml
+
+      - name: Install dependencies
+        run: pnpm install --frozen-lockfile
+
+      - name: Typecheck
+        run: pnpm typecheck
+
+      - name: Lint
+        run: pnpm lint
+
+      - name: Check formatting
+        run: pnpm format:check
+
+      - name: Test
+        run: pnpm test
+
+      - name: Build
+        run: pnpm build