Fix preview deployment by removing external package

[benadamstyles]

resolves #310
reverts #282

Component / Package Name:

This PR contains:

• bugfix
• feature
• refactor
• documentation
• other

Are tests included?

• yes (bugfixes and features will not be merged without tests)
• no

I haven't added tests because you don't already have any for previewing (AFAICT) and I can't even begin to think how I would add them from scratch.

Breaking Changes?

• yes (breaking changes will not be merged unless absolutely necessary)
• no

Description

Externalising react/jsx-runtime makes it impossible to serve the built preview app to any browser. It seems #282 did this to fix the preview dev server, but I don't have any issues running the dev server locally after making my change.

[shellscape]

That's going to reintroduce the React 19 issue with the preview server. That was a real problem. The right fix should probably involve determining which context the build is happening in, and removing it logically.

[benadamstyles]

Are you sure? I ran the preview server locally with React v19.1.0 and it was fine.

[benadamstyles]

In fact it seems to me like the real issue is the fact that the server depends on the developer's version of React as a peer dependency, instead of having its own version defined in package.json. That would mean you could control exactly what React internals are available.