🎨 feat: Add Save/Download button to Artifact and CodeBlock as request…

[Ringish]

Summary

This PR adds a "Save" button to both the Artifact and CodeBlock components, allowing users to download code directly instead of just copying it to the clipboard.

Motivation and Context

• Users previously had to manually copy or click Copy button and paste code
• This feature improves usability by enabling direct downloads
• The implementation uses showSaveFilePicker() when available, with a fallback to an anchor-based download

Closes #4645

Change Type

• New feature (non-breaking change which adds functionality)

Testing

1. Navigate to an artifact or a code block in the app
2. Click the new "Save" button
3. Verify that the correct file is downloaded

Checklist

• My code adheres to this project's style guidelines
• I have performed a self-review of my own code
• I have commented in any complex areas of my code
• I have made pertinent documentation changes
• My changes do not introduce new warnings
• [] I have written tests demonstrating that my changes are effective or that my feature works
• Local unit tests pass with my changes
• A pull request for updating the documentation has been submitted (if needed)

[danny-avila]

Thanks, implemented in #5428