Static autoloop testing surfaced a SuggestSwaps failure when the
planner disqualified a custom asset channel.
Add the missing AutoReason enum value and handle ReasonCustomChannelData.
Extend the public rpc surface for static autoloop integration
without turning the planner on yet. SuggestSwaps responses can
now carry static-address loop-in requests and the new planner
reason for missing static candidates is mapped over rpc.