9dd5e8dbac
Address review findings from sonnet-review-bot (review 3086): - PostReview now returns ErrConflictingCommitIDs when comments specify different non-empty CommitIDs, since the GitHub API accepts only a single commit_id per review. Previously the discrepancy was silently ignored, using only the first commit's ID. - Extract newTestClient into helpers_test.go to make cross-file sharing between review_test.go and identity_test.go explicit. Refs: #81