Support Vercel deploy target for CLI docs website (getsentry/toolkit)

[jared-outpost]

Part of the sentry-cli + sentry-mcp -> getsentry/toolkit monorepo merge.
Full plan: https://gist.github.com/BYK/8c0ce6cec64608f41fe5654b7827228e

Follow-up to #842. We've decided to deploy the CLI docs website
to Vercel instead of Cloudflare, so we need the Craft equivalent of the
Cloudflare target (#843) for Vercel.

Ask

The merged toolkit monorepo needs to deploy the CLI documentation website to
Vercel as a release-gated step (docs must stay in sync with the published
CLI version — same guarantee the current gh-pages Craft target provides).
GitHub Pages doesn't scale to multiple sites in one monorepo, so the CLI website
is moving to Vercel. We want to drive this from Craft on CLI release.

Question / request for Craft

• Does Craft have (or would it accept) a vercel target invoking the Vercel
  CLI / Deploy API to promote a prebuilt docs artifact to production, gated to
  release tags?
• If not, confirm the recommended pattern for a custom / command-style
  target invoking vercel deploy --prod with VERCEL_TOKEN +
  VERCEL_ORG_ID / VERCEL_PROJECT_ID, gated to release tags, consuming a
  prebuilt docs artifact.
• Confirm this composes with the prefixed release tags work
  (cli@x.y.z / mcp@x.y.z, feat: support prefixed tags for monorepo multi-product releases #844) for per-product .craft.yml
  invocation.

Cross-links

• Supersedes the Cloudflare approach in Support Cloudflare deploy target + prefixed multi-product releases (for getsentry/toolkit) #842 for the CLI docs site
• Master: toolkit merge: CLI docs website to release-gated Vercel cli#1245

[BYK]

Let's get this done Jared