feat: shell_screenshot should return all file paths including SVG

[dwmkerr]

Summary

The shell_screenshot tool currently returns a single download_url for the PNG file. It should also return the SVG path since we generate both formats internally.

Proposal

Return all generated file paths in the response:

{
  "png_url": "http://localhost:7498/files/.../screenshot.png",
  "svg_url": "http://localhost:7498/files/.../screenshot.svg"
}

This gives users flexibility to use either format - SVG for scalability, PNG for compatibility.

Related

This should also be considered for inline/base64 output (#43) - offer both PNG and SVG inline options.