Extends the JSON API with a route to check whether a given peer ASN
is authorized as an upstream provider for a customer ASN, mirroring
the existing peer-check already available on the HTML lookup page.
Response is a superset of the existing /api/aspa/{asn} shape, adding
peer and authorized fields.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01SdWQ3jVyzwRoQjVfAfK4mZ