chore: isolate docs from root workspace

Remove docs from root workspace packages since it already has its own
pnpm-workspace.yaml for independent Netlify builds. Move vitepress
peer dep rule to docs workspace config. Add docs lockfile for
reproducible installs.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: branchseer