Sandbox: Override the right vitest.config file depending on language

[valentinpalkovic]

Closes #

What I did

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

This section is mandatory for all contributions. If you believe no manual test is necessary, please state so explicitly. Thanks!

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

Updates sandbox-parts.ts to correctly handle Vitest configuration files based on the project's language, ensuring TypeScript and JavaScript sandboxes get the appropriate vitest.config file extensions.

• Modified setupVitest function to use .ts or .js extensions based on sandbox language type
• Prevents TypeScript config files from being used in JavaScript sandboxes which could cause test execution issues
• Aligns with existing Vitest setup patterns shown in .storybook/vitest.setup.ts documentation
• Improves integration test reliability by using language-appropriate configuration files

[greptile-apps]

LGTM

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[nx-cloud]

View your CI Pipeline Execution ↗ for commit 7e01aab.

Command	Status	Duration	Result
nx run-many -t build --parallel=3	✅ Succeeded	1m 11s	View ↗

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☁️ Nx Cloud last updated this comment at 2025-06-17 14:00:59 UTC

[nx-cloud]

View your CI Pipeline Execution ↗ for commit 7e01aab.

Command	Status	Duration	Result
nx run-many -t build -c production --parallel=3	✅ Succeeded	2s	View ↗

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☁️ Nx Cloud last updated this comment at 2025-06-17 13:56:22 UTC