add GitHub workflow

.github/workflows/check.yaml

@@ -0,0 +1,18 @@
+- name: Check
+- on:
+    workflow_dispatch:
+    pull_request:
+    push:
+      branches:
+        - main
+- jobs:
+    check:
+      runs-on: macos-latest
+      # TODO Xcode versions (multiple?)
+      steps:
+        - uses: actions/checkout@v4
+        - npm ci
+        - script/format/check
+        - script/lint/check
+        - swift build
+        - swift test