getSurfaceEloMap now joins through season_participants and returns
rows keyed by seasonParticipantId (was participantId).
batchUpsertSurfaceElos now performs a second db.select to resolve
canonical links before mirroring writes; tests mock the lookup
explicitly and exercise both the "no canonical link" short-circuit
path and the "mirror to canonical" path.
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
879c09a38d