fix: address sonnet review MINOR findings (#2916)

- client.go: fix misleading timer.Stop() comment (finding #1)
- pr.go: document all-or-nothing semantics for GetCommitStatuses
  when check-runs endpoint fails after statuses succeed (finding #2)
- files.go: include both array and object unmarshal errors in
  ListContents fallback error message (finding #3)
- pr.go: expand mapCheckRunStatus comment to explain non-blocking
  policy decision (finding #4)

github/pr.go

@@ -127,6 +127,9 @@ func (c *Client) GetPullRequestFiles(ctx context.Context, owner, repo string, nu
 // Returns nil (not an empty slice) when there are no statuses or check runs.
 // If the commit statuses endpoint fails (e.g. 404 for an unknown SHA), the
 // function returns immediately without attempting the check-runs endpoint.
+// If the check-runs endpoint fails after statuses were fetched successfully,
+// the function returns an error (not a partial result) so callers always get
+// either a complete view or a clear error signal.
 func (c *Client) GetCommitStatuses(ctx context.Context, owner, repo, sha string) ([]vcs.CommitStatus, error) {
 	var result []vcs.CommitStatus
 
@@ -192,7 +195,7 @@ func mapCheckRunStatus(conclusion *string) string {
 	case "failure", "action_required", "timed_out":
 		return "failure"
 	case "cancelled", "skipped", "neutral":
-		return "success" // non-blocking
+		return "success" // non-blocking: these do not indicate a blocking failure per GitHub check suite semantics
 	case "stale", "waiting":
 		return "pending"
 	default: