feat(federation): relay agreements and our zone list to the operator

The portal needs these so an operator can grant a partner zones without
kubectl. Three operator-only routes relay to FM like the partner registry:
POST /platform/v1/federation/agreements, PATCH .../agreements/{agreementId}
and GET .../local-zones. GET .../partners/{partnerOpId} now declares the
agreements FM embeds in the partner detail; a detail without them still
passes.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>