New "restricted" risk rating and clearer country info example

Broker API

Adds restricted to the crypto_risk_rating and securities_risk_rating enums on the country info schema.

• The 200 response example now shows ISO 3166-1 alpha-3 country codes as top-level keys, matching the dictionary shape actually returned.
• The wire contract is unchanged.

Affected Endpoints

• GET /v1/country-info