Add description for docs-sandpack skill

[NA-V10]

Summary

Closes #8382

Added a more descriptive summary for the docs-sandpack skill to improve Dispatch matching and make the skill easier to discover.

The updated description now mentions common Sandpack use cases such as:

• Interactive code examples
• Live React playgrounds
• Multi-file demos
• Line highlights
• Expected errors
• External dependencies

Also added a short introductory paragraph below the frontmatter to explain what the skill covers and when it should be used.

How was this tested?

• Verified that the updated frontmatter remains valid
• Confirmed that the new description is concise and matches the style of surrounding skill files
• Checked that the introductory paragraph appears correctly before the # Sandpack Patterns section

[meta-cla]

Hi @NA-V10!

Thank you for your pull request and welcome to our community.

Action Required

In order to merge any pull request (code, docs, etc.), we require contributors to sign our Contributor License Agreement, and we don't seem to have one on file for you.

Process

In order for us to review and merge your suggested changes, please sign at https://code.facebook.com/cla. If you are contributing on behalf of someone else (eg your employer), the individual CLA may not be sufficient and your employer may need to sign the corporate CLA.

Once the CLA is signed, our tooling will perform checks and validations. Afterwards, the pull request will be tagged with CLA signed. The tagging process may take up to 1 hour after signing. Please give it that time before contacting us about it.

If you have received this in error or have any questions, please contact us at cla@meta.com. Thanks!

[github-actions]

Size changes

Details

📦 Next.js Bundle Analysis for react-dev

This analysis was generated by the Next.js Bundle Analysis action. 🤖

This PR introduced no changes to the JavaScript bundle! 🙌