Introduce a PR tab in the explorer sidebar that shows status checks,
reviews, and the merged timeline for the current branch's pull
request. Extend checkout PR status with number, draft flag, repo
identity, and per-check workflow/duration; add a new
pull_request_timeline request/response pair backed by a GraphQL
query; enrich the workspace git snapshot to carry the fields through
to the client; and extend the checkout-git-actions store so timeline
queries are invalidated alongside status when mutations land.
e373c33108