Verify sibling citation-engine checkout, link dependency resolution,
toolchain, and absence of stale in-repo engine copies. Prints actionable
fix hints when the installation layout is wrong.
`make preview` runs `pnpm build && pnpm preview` so the demo can be
served from the production bundle at http://localhost:4173/. Plus
convenience targets for dev, build, test, typecheck, lint.
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
