chore: document workflows and deduplicate LICENSE files
Add header comments to publish.yml and preview-website.yml explaining
non-obvious implementation details like multi-tag matrix publishing,
npm usage for provenance, and dynamic wrangler.json injection.
Also, expand on the publish verification process in CONTRIBUTING.md.
Finally, replace duplicate LICENSE files in packages with symlinks to root
so when 2027 comes around, there is less maintenance.