Register did:oan DID method.

This commit adds the did:oan DID method registration for OpenAgenet (OAN).
OAN adopts did:oan as the identifier method for an agent identity governance
system that supports trusted agent registration, root-governed lifecycle
management, authorization-aware discovery, and verifiable infrastructure-node
authorization.

The method specification describes how OAN identifiers are represented,
resolved, governed, and used across OAN roles such as agents, registrars,
discovery services, root services, and future third-party credential issuers.
The registered verifiable data registry is the OAN root-governed registry and
its blockchain-backed authorization bulletin, which together provide the
trusted publication and lifecycle state used by OAN participants.

The registration points to the public OAN DID method specification maintained
under the OpenAgenet public documentation repository.

Author: wolfbrother

methods/oan.json

@@ -0,0 +1,9 @@
+{
+  "name": "oan",
+  "status": "registered",
+  "verifiableDataRegistry": "OpenAgenet root-governed registry and blockchain-backed authorization bulletin",
+  "contactName": "OpenAgenet (OAN)",
+  "contactEmail": "xujinliang@caict.ac.cn; jlxufly@gmail.com",
+  "contactWebsite": "https://github.com/OpenAgenet",
+  "specification": "https://github.com/OpenAgenet/oan-public-docs/blob/main/did-oan-specs/doc/OAN%20DID%20Method%20Specification.md"
+}