Exposes a CommentService method that maps a collection of
commentIds to their annotationIds via commentRepository.findAllById.
Unknown comments and comments with null annotationId are omitted.
Used by the dashboard activity feed enrichment to supply the
deep-link annotationId without growing the audit SQL query.
Refs #300.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>