Ensure Dockerfile is compatible with Smithery

[JoshMock]

Smithery server setup is currently failing. The docs say:

We only support Linux Docker images on major distros (Alpine/Debian-based) and expect sh to run in your container. Other distros are untested and may not deploy.

We're using a Wolfi image, which should theoretically work, but may need to have sh manually installed on it to work with Smithery.