Actually automatically update vscode extension

The readme claims "This repo now automatically tracks upstream surfer." which is not true. It still has to be manually built and published to the extension marketplace; there is no CI job. It was last updated on 2025-05-08.

I think it would make sense to move this into the surfer/ repo to simplify CI, then have a CI job upload a prerelease on every merged commit, and publish corresponding versions for major and minor surfer versions.