DID document update fallback for git service registration

[LiranCohen]

Summary

When the agent does not support DID document updates, registerGitService() in src/git-server/did-service.ts logs a warning and silently skips registration. The git-remote-did helper then has no way to discover the git endpoint.

Location

src/git-server/did-service.ts lines 45–50:

console.warn(
  'Agent does not support DID document updates. ' +
  'GitTransport service not registered. ' +
  'The git-remote-did helper will need a DWN endpoint fallback.',
);

Expected behavior

Implement a fallback mechanism so that git-remote-did can discover the git transport endpoint even when the DID document cannot be updated. Options:

1. DWN record fallback — store the git endpoint URL in a well-known DWN record that resolveGitEndpoint() checks as a third priority after GitTransport and DecentralizedWebNode service types
2. Configuration file — allow users to specify git endpoint mappings in a local config
3. Environment variable — DWN_GIT_ENDPOINT override for local development

Impact

Affects did:jwk and other DID methods that don't support document updates. Users with these DID methods cannot register their git endpoint for remote discovery.