[pi-extension] Packaging & Distribution

[codenamekt]

Overview

Make the pi-extension easy to install and distribute.

Issues to Address

• No npm package for pi extension — create hexus-pi npm package that installs extension + config
• No install script — add npx hexus-pi install to bootstrap config, handle existing configs gracefully
• No Docker compose snippet — add hexus-extension service to example docker-compose in docs
• No version sync — extension version should match hexus version for compatibility

Acceptance Criteria

• npm install hexus-pi installs extension to ~/.pi/agent/extensions/hexus
• npx hexus-pi install --api-url http://localhost:8000 bootstraps config with provided URL
• Docker compose example in docs shows hexus + pi working together
• Extension reads HEXUS_VERSION env var and logs warning on mismatch