Docs: Mention React version requirement for addons

[Sidnioulz]

What I did

Clarified that addons must align their React version w/ Storybook, and must be externally packaged if users use a different React version in their preview code. I did this in a way that doesn't explicitly mention versions to avoid the callout expiring upon future releases.

This should address user feedback received via Chromatic about running custom addons in React 19 codebases.

Checklist for Contributors

Testing

N/A

Documentation

• Add or update documentation reflecting your changes

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 publish.yml --field pr=<PR_NUMBER>

Summary by CodeRabbit

• Documentation
  • Added guidance clarifying that UI addons must use the same React version as Storybook, with recommendations for using standalone addons when versions differ.

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[coderabbitai]

📝 Walkthrough

Walkthrough

Documentation update adding informational callout blocks about UI addon React version compatibility requirements in Storybook, inserted in two locations within the writing-addons guide.

Changes

Cohort / File(s)	Summary
Documentation - Addon Version Requirements docs/addons/writing-addons.mdx	Adds info callouts advising that UI addons must use the same React version as Storybook, with suggestion to use standalone addons via Addon Kit if versions differ. Callouts inserted in two locations: after initial code snippet and within UI-based addons setup section.

Estimated code review effort

🎯 1 (Trivial) | ⏱️ ~2 minutes

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[Sidnioulz]

List to currently supported version (package.json of addon-kit)