feat(r2): grant partners an agreement before federating

A partner only sees our zones if an agreement grants them, and it learns
them from the CreateFederation answer, so the agreement has to exist first.
Each oop_platform_partners entry takes an optional agreement (zone names,
GSMA terms, allowed requests); fm_partners.py resolves the names through SRM
and creates it before federating. A changed agreement replaces the active one,
which is suspended; an unchanged one is left alone. The federate scenario
grants oop_platform_partner_agreement to every partner it finds.

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