fix: restore empty_node_modules volume

[focusaurus]

Impact: minor
Type: bugfix

Issue

I removed this volume mount in some prior work not understanding it's necessity.

Solution

Add it back with a comment justifying its existence.

Breaking changes

N/A

Testing

1. Bring up storefront (especially on mac)
2. Locally run yarn on your host
3. Configure your editor to use the project-specific eslint
4. Confirm IDE/editor based linting works OK from host OS
5. Confirm app runs fine in docker at same time

[willopez]

Tested locally and inside the container and works fine.