feat(01-01): add RankingSnapshot model + enums to schema.prisma
- Add RankingTriggerType enum (MANUAL, AUTO, RETROACTIVE, QUICK)
- Add RankingMode enum (PREVIEW, CONFIRMED, QUICK)
- Add RankingSnapshotStatus enum (PENDING, RUNNING, COMPLETED, FAILED)
- Add RankingSnapshot model with roundId/triggeredById FKs, criteria/results JSON fields, AI metadata
- Add Round.rankingSnapshots back-relation (RoundRankingSnapshots)
- Add User.rankingSnapshots back-relation (TriggeredRankingSnapshots)
- Create migration 20260227000000_add_ranking_snapshot
- Regenerate Prisma client (prisma.rankingSnapshot accessible)