npm publish for npx/bunx

[johnnyhuy]

Summary

• Publish npm package for npx and bunx usage.

Context

• npx and bunx provide zero-install UX for Node/Bun environments.

Scope

• Add package.json bin entry and publish package.
• Ensure CLI behavior matches compiled binaries.
• Document npm publish and update flow.

Out of scope

• Auto-downloading platform binaries from npm (later).

Acceptance criteria

• npx skillet and bunx skillet run the CLI successfully.