InviteToFamily previously rejected any second invitation for a (family, node)
pair with PendingInvitationAlreadyExists, even once the existing invitation had
expired and was left inert in the pending map. Now a still-valid invitation still
blocks a duplicate, but an expired one is archived under the new terminal status
FamilyInvitationStatus::Expired and superseded by the fresh invitation.
Regenerated the contract JSON schema and updated the openspec capability.
Jędrzej Stuczyński
c85fb161d4