Apply the React JSX transform consistently in Workbench preview-build exports

Overview

The preview-build command of @drupal-canvas/workbench can generate component mock HTML that fails at runtime with ReferenceError: React is not defined.

The failure is caused by the standalone mock export bundling path compiling some discovered JSX component entries to React.createElement(...) without applying the same React JSX transform as the main Workbench app.

A consistent reproduction is:

1. Create a component with a mocks.json file so preview-build generates component-mock-01.html.
2. Add another previewable discovered component with a .jsx entry file that uses top-level JSX without importing React, for example:

   const badge = <span>Logo</span>;
   
   export default function Logo() {
     return badge;
   }
   

3. Run canvas-workbench preview-build --component-path <component.yml> --out-dir <dir>.
4. Open the generated component-mock-01.html.
5. The page fails at runtime with ReferenceError: React is not defined.

This affects mock exports because they bundle all discovered previewable component sources, not only the selected component. As a result, an unrelated discovered JSX component can break the exported mock HTML.

Proposed resolution

Update the standalone interactive preview bundler used by preview-build to include the React Vite plugin, so exported preview HTML uses the same JSX transform behavior as the main Workbench app.

User interface changes

n/a