[ty] Extend the review skill to local changes (#29509)
`review-ty-pr` currently assumes every review targets a pull request.
Extend it to cover local changes, including staged and unstaged edits,
branches compared with their base, and changes just written by a user or
an agent.
To avoid executing untrusted code on the host, require untrusted code
and code of uncertain trust to be vetted and run offline in a disposable
container. Allow host testing when the checkout, dependencies, inputs,
and commands are trusted; if vetting or isolation is unavailable, the
affected review work remains static.
The skill also clarifies how to assess typing-spec conformance and
ecosystem impacts, judge whether tests are necessary, and handle
test-generated snapshot updates.
