did:nostr integration: use the DID document as a lookup tier

[melvincarvalho]

did:nostr (https://did-nostr.com) resolves a pubkey to a DID document at https://<resolver>/.well-known/did/nostr/<pubkey>.json, which can list the user's relays as service endpoints.

Use this as a discovery tier in resolution:

1. Resolve the DID document for the pubkey
2. Read the relay service endpoints to learn where to find the user's kind 31034 DNS event
3. Query those relays for the record set

The dnstr CLI already resolves via did:nostr for the website mapping; this extends it to relay discovery for the decentralized DNS path (#2, #3).