feat: migrate release automation workflow to pnpm

[somhairle-marisol]

Summary

• migrate the workspace and release automation from npm to pnpm
• add a publishable @clinwise/release-scribe demo package for GitHub Packages validation
• combine Changesets and git-cliff so version PRs, root changelog updates, and publish steps share one flow
• document required GitHub Actions permissions for the release workflow

Validation

• CI=true pnpm install --frozen-lockfile
• pnpm lint
• pnpm test
• pnpm build
• npm pack --dry-run --cache /tmp/npm-cache ./packages/release-scribe
• pnpm run changeset:version
• pnpm changeset publish for @clinwise/release-scribe@0.1.0