Foundation layer for unified service client wrappers: - AuthMethod enum (None, Bearer, Header, Token) - ServiceClient trait with service_name(), base_url(), from_parts() - HttpTransport with json(), json_opt(), send(), bytes() helpers - SunbeamClient lazy factory with OnceLock-cached per-service clients - Feature flags for all service modules (identity, gitea, matrix, etc.) Bump: sunbeam-sdk v0.2.0