Use baseline instead of browserslist to set build targets

[stipsan]

Vite v7 has changed its build target defaults to match baseline-widely-available. It's generated ahead of time, using a set date as the target. The date is only updated on each major of vite.

This seems like a better model for us. It removes the need to have a browserslist key in package.json that specifies @sanity/browserslist-config.