types: add MarshalZerologObject to domain types
Implement zerolog.LogObjectMarshaler interface on domain types
for structured logging:
- Node: logs node.id, node.name, machine.key (short), node.key (short),
node.is_tagged, node.expired, node.online, node.tags, user.name
- User: logs user.id, user.name, user.display, user.provider
- PreAuthKey: logs pak.id, pak.prefix (masked), pak.reusable,
pak.ephemeral, pak.used, pak.is_tagged, pak.tags
- APIKey: logs api_key.id, api_key.prefix (masked), api_key.expiration
Security: PreAuthKey and APIKey only log masked prefixes, never full
keys or hashes. Uses zf.* constants for consistent field naming.
cf3d30b6f6