Set `main` attribute in headless package.json back to the dist file
Otherwise the prod webpack build is built in a different way so that:
1. runtime object assignments (e.g. `Object.assign(api, foo)`) aren't
reflected on imported objects (causing undefined attribute errors).
2. circular imports cause crashes, making the build unusable.
Unfortunately fixing these issues on a more fundamental level will
require much more work.
JC Brand