Refactor docs and release workflows to use pnpm where possible

[willgriffin]

Summary

The repo is already a pnpm monorepo, but the docs subproject and parts of the publish workflow still go through npm. That split makes CI harder to reason about and recently contributed to runner cache pressure during publish.

Failing run for context:

• https://github.com/happyvertical/smrt/actions/runs/23687428351/job/69009627797

Scope

• Move docs/ onto pnpm instead of its own npm lockfile flow
• Add docs to the pnpm workspace if that is the cleanest path
• Replace npm install / npm run --prefix docs ... workflow steps with pnpm equivalents
• Remove docs/package-lock.json once the docs flow is fully pnpm-managed
• Audit root scripts that still shell out to npm for docs commands and convert them to pnpm

Important note

changeset publish can publish with pnpm in a pnpm repo, but Changesets still shells out to npm for some registry metadata/auth operations (npm info, npm profile get). So this issue is about moving the repo-owned docs/release workflow pieces to pnpm where possible, not fully removing npm from the release environment.

Acceptance criteria

• docs/ no longer depends on package-lock.json
• Docs install/build/dev commands run through pnpm
• Publish/docs workflows no longer call npm for repo-managed install/script execution where pnpm can be used instead
• CI passes with the new workflow