onGitHubPullRequestReadyForReview emits the "ready_for_review" transition from draft to reviewable.
automations/watch-reviewable-github-pull-requests.automation.ts
account defaults to the project binding. Returns Signal<GitHubPullRequestReadyForReviewEvent> with action: "ready_for_review" and the complete typed payload. Opening a pull request that was never a draft does not emit this trigger.