Prepare for GitHub Marketplace publishing

[nev-offload]

Problem

To make the action discoverable and easy to adopt, it should be published to the GitHub Actions Marketplace.

Requirements

• action.yml has proper branding (icon, color)
• README follows marketplace conventions (badges, screenshots, feature list)
• Action is tagged with semver releases (v1, v1.0.0)
• Action is tested on multiple repo types (JS, Python, Rust, etc.)
• CHANGELOG.md exists
• LICENSE is appropriate (MIT?)
• Repository is public
• Marketplace listing description and categories are set
• Action uses @vercel/ncc or similar to bundle (so users don't need npm install)

Publishing steps

1. Create a release with a semver tag
2. Go to repo settings → "Publish this Action to the GitHub Marketplace"
3. Fill in listing details
4. Submit for review

Priority

P3 — Long-term goal. Get the action working well first.