fix(ci): Use base SHA for production deployment lookup in versioned docs aliasing (#11450)
## Summary
- Uses the base SHA (the commit on `main` that the release started from)
instead of the tag SHA for finding the production deployment
- Adds `target=production` filter to ensure only production deployments
are aliased
- Removes unnecessary git tag fetching since we no longer look up the
tag
## Background
The previous fix (#11449) added `target=production` to the Vercel API
query, but was still using the wrong SHA. The tag points to a commit on
the staging branch, not the original commit on `main` that has the
production deployment.
This fix captures the base SHA before any staging commits are made and
passes it to the `alias-versioned-docs` job.