Radar Connect Shopify Official

Attach an offline Shopify Admin token to a user's own RadarShop.

Called by the embedded Shopify app (tintin-shopify-radar) after install: its own OAuth already produced an offline token, so instead of sending the merchant through Radar's second OAuth it hands the token over here. Writes through the same upsert as the OAuth callback (radar_shopify.store_official_connection) — encrypted token, scanning status, next scheduler cycle picks it up.

Body: {user_id, shop_domain, access_token, scopes?}. X-Internal-Key gated, like every other internal endpoint.