Publish Claudius to npm under @pmds/claudius

[PAMulligan]

Goal

Make Claudius installable via npm so consumers can npm install @pmds/claudius rather than vendoring the widget from the repo.

Acceptance criteria

• Configure package.json exports map (ESM + CJS + types)
• Add prepublishOnly build script
• Set up npm provenance via GitHub Actions
• Publish first version to npm
• Add install instructions to README

Milestone

v1.2.0