Core: Fix bundling of React

[yannbf]

Relates to #29805

What I did

This PR undoes the work done in #28541 which actually caused the react globalization logic to stop working in Storybook 8. This should allow users to use React 19 in preview while React 18 is used in the manager.

Checklist for Contributors

Testing

The changes in this PR are covered in the following automated tests:

• stories
• unit tests
• integration tests
• end-to-end tests

Manual testing

• Build a react 19 sandbox
• Add a manager.tsx file with the following content:

import React from 'react';
import { addons, types } from '@storybook/manager-api';

addons.register('test', () => {
  addons.add('test', {
    type: types.TOOLEXTRA,
    title: 'test',
    paramKey: 'test',
    render: () => {
      return <>test</>
    },
  });
});

• Inspect the generated manager-bundle file, make sure React is globalized and not bundled in

Documentation

• Add or update documentation reflecting your changes
• If you are deprecating/removing a feature, make sure to update
  MIGRATION.MD

Checklist for Maintainers

• When this PR is ready for testing, make sure to add ci:normal, ci:merged or ci:daily GH label to it to run a specific set of sandboxes. The particular set of sandboxes can be found in code/lib/cli-storybook/src/sandbox-templates.ts

• Make sure this PR contains one of the labels below:

  Available labels

  • bug: Internal changes that fixes incorrect behavior.
  • maintenance: User-facing maintenance tasks.
  • dependencies: Upgrading (sometimes downgrading) dependencies.
  • build: Internal-facing build tooling & test updates. Will not show up in release changelog.
  • cleanup: Minor cleanup style change. Will not show up in release changelog.
  • documentation: Documentation only changes. Will not show up in release changelog.
  • feature request: Introducing a new feature.
  • BREAKING CHANGE: Changes that break compatibility in some way with current major version.
  • other: Changes that don't fit in the above categories.

🦋 Canary release

This PR does not have a canary release associated. You can request a canary release of this pull request by mentioning the @storybookjs/core team here.

core team members can create a canary release here or locally with gh workflow run --repo storybookjs/storybook canary-release-pr.yml --field pr=<PR_NUMBER>

Greptile Summary

This PR reverts changes to JSX compilation settings in the React addon to fix React globalization logic in Storybook 8, enabling React 19 support in preview while maintaining React 18 compatibility in the manager.

• Modified code/core/assets/server/addon.tsconfig.json to revert JSX compilation mode from 'react-jsx' back to 'react'
• Maintains jsxImportSource setting as 'react' for compatibility
• Undoes changes from PR Core: Fix manager-builder tsconfig to emit react-jsx #28541 that broke React globalization logic
• Enables React 19 support in preview while keeping React 18 in manager

[greptile-apps]

LGTM

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