pull_request gives fork PRs a read-only token, so the sticky comment can't be
posted from pr-title.yml. Split the comment into pr-title-comment.yml
(workflow_run), which runs from the base branch with a write token and works for
forks. pr-title.yml stays the required check (runs on the PR branch, forks
included, no deadlock) and hands the lint result to the commenter via an
artifact. workflow_run only fires once this workflow is on the default branch, so
it activates for fork PRs after merge; the required check is unaffected.
