Add config server client support for the C FFI and Android JNI bindings.
Reuse the existing easytier::web_client::run_web_client path and
NetworkInstanceManager; OHOS is unchanged.
Report successful remote config apply/delete operations through a
callback, with one JSON event per affected instance.
Keep the config server client and FFI data plane mutually exclusive: once
either side is in use, the other side returns an error instead of sharing
lifecycle state.
KKRainbow