Produces a tailored Sanity Studio upgrade plan by inspecting the repository's installed versions, config, and source, then reporting only the breaking changes that actually apply. Covers Studio v3 and later; v2 projects are identified and redirected, not planned. Use this skill whenever someone wants to upgrade, migrate, or modernize a Sanity Studio across one or more major versions from v3 onward, asks what will break if they bump the `sanity` package, asks why their Studio broke after an upgrade, or asks how far behind their Studio is. Triggers on "upgrade sanity studio", "migrate our studio to v6", "bump sanity", "what breaks if we upgrade", "our studio is on an old version", "sanity upgrade plan", "is our studio out of date", "we are several majors behind". DO NOT load for upgrading non-Sanity dependencies, for Content Lake `apiVersion` questions, for content or schema migrations that change documents, or for setting up a new Sanity project.