Module core/auth

@honua/sdk-js/auth — pluggable HonuaAuthProvider built-ins and the CredentialStore abstraction.

These providers plug into new HonuaClient({ auth }) and are therefore attached and refreshed transparently across all transports the client drives — every REST fetch path and every gRPC-web call (the client's auth interceptor re-resolves credentials per attempt), plus the 401/403 force-refresh retry.

This module is a dedicated subpath so a HonuaClient-only consumer never pays the PKCE/token-exchange code size unless they opt in.