ci: add code coverage check & badge

.github/workflows/ci.yaml

@@ -15,6 +15,7 @@ jobs:
       - run: npm install
       - run: npm test
       - run: xvfb-run --auto-servernum npm run e2e
+      - run: bash <(curl -s https://codecov.io/bash)
       - run: npm run build:prod
         env:
           CI: true