ci: add verify workflow for lint, typecheck, and build

.github/workflows/ci.yml

@@ -0,0 +1,41 @@
+name: CI
+
+on:
+  pull_request:
+    branches: [main]
+  push:
+    branches: [main]
+
+# A newer push to the same branch makes the in-flight run obsolete.
+concurrency:
+  group: ci-${{ github.ref }}
+  cancel-in-progress: true
+
+permissions:
+  contents: read
+
+jobs:
+  verify:
+    name: verify
+    runs-on: ubuntu-latest
+
+    steps:
+      - uses: actions/checkout@v7
+
+      - uses: actions/setup-node@v7
+        with:
+          node-version: 22
+          cache: npm
+
+      - name: Install
+        run: npm ci
+
+      # Next 16 dropped linting from `next build`, so it runs on its own here.
+      - name: Lint
+        run: npm run lint
+
+      - name: Typecheck
+        run: npm run typecheck
+
+      - name: Build
+        run: npm run build