Bug Report

The MDX docs state one should be able to declare variables within the MDX document through export like so:

import { Playground } from 'docz';

export const myVariable = 'Yay!'
# Hello, world!
<Playground>
  <div>{myVariable}</div>
</Playground>

To Reproduce

1. create-docz-app my-docz-app && cd my-docz-app
2. Change src/index.mdx to above example
3. Run npm run docz dev
4. See error in browser:

❌ Uncaught ReferenceError: myVariable is not defined

Expected behavior

It should render <div>Yay!</div> and variable myVariable should be available in Playground