Check gh auth identity before posting PR review feedback

When asked to post review comments on a PR, run gh auth status first. If an agent authored the PR from the same account the CLI is authenticated as, the review posts as the author — which silently misattributes a reviewer's decisions to the submitter. GitHub also blocks approve and request-changes on your own PR (a COMMENT-type review is allowed), so gh pr review --approve/--request-changes errors while gh pr comment always works. Cross-check the gh login against the PR author and the local git user.email; they can differ even when the human is the same person, because agents commit under a different email than the GitHub account name suggests.