Find the curated-list entry whose block (entry line plus indented
sub-bullets) mentions prUrl on a STATUS-marked line, and return the
entry line's own GitHub URL — the URL markIssueAsDone needs to locate
the block again.
Returns undefined when no entry block mentions the PR URL on a marked line, or when the mentioning block's entry line carries no GitHub URL (nothing for the mark-done transform to anchor on).
Daily merge-loop reconciliation — auto-mark curated-list entries whose PR merged (#1463).