feat: Support automatic artifact storage for files generated by skill toolset scripts

[henrywang0314]

Summary

When skill toolset scripts generate files (e.g., PDF creation, image generation, data
exports), these files are created in temporary directories and lost after execution.
There's currently no built-in mechanism to persist skill-generated files as artifacts.

Current Behavior

• Skill scripts can generate files in temporary directories during execution
• These files are not automatically saved as artifacts
• SaveFilesAsArtifactsPlugin only handles user-uploaded files (inline_data)
• Files are discarded after script execution completes

Expected Behavior

One or more of:

1. Automatic artifact storage for skill-generated files (if returned in response)
2. Plugin support for intercepting tool responses with file data
3. Documentation on best practices for persisting skill-generated files
4. Skill API extension for explicit artifact saving

Use Cases

• PDF generation skills that need to save generated PDFs
• Image processing skills that output images
• Data processing skills that generate reports or exports
• Any skill that creates files meant to be accessed later

Example Scenario

# PDF skill script generates a file
# Expected: File automatically becomes available as artifact
# Actual: File is lost after script execution

[klateefa]

@henrywang0314 Thanks for the update. The request is currently being reviewed, and I will let you know if anything further is needed. Thank you for your understanding.