Delegates to FeedbackRepository.list_by_run via the existing _resolve_run
helper; includes tests for success, 404, empty list, and 503 (no DB).
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
New endpoint resolves thread_id from the run record and delegates to
RunEventStore.list_messages_by_run for cursor-based pagination.
Ownership is enforced implicitly via RunStore.get() user filtering.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>