Add library/channels_api over the reliable-channel logic: channel_create
returns a {.ffiHandle.} ReliableChannelHandle, channel_send/channel_close
operate on it, and the channel message received/sent/error events are fed by
the channel-layer broker events. Wire them into the FFI root.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
