follow-up: create TriageNodeRow type and plumb through Repository hierarchy #573
Description
Deferred from PR #554 review.
Context: findNodesForTriage currently returns NodeRow[], but triage queries return additional computed columns (fan-in, complexity, etc.) that don't exist on the base NodeRow type. A dedicated TriageNodeRow type should be created in src/types.ts and used as the return type across Repository, SqliteRepository, and InMemoryRepository.
This was acknowledged as scope creep during the #554 review and deferred, but never tracked.