Handle Kyoto node thread startup and exit failures

`CbfNode::run` currently builds a Tokio runtime with `unwrap()` and discards the result of `node.run().await`.

This can abort the process when runtime setup fails and reduces terminal node errors like `NoReachablePeers` to a generic `NodeStopped`.

Start at CbfNode::run and inspect how the Tokio runtime is built and how node.run().await returns its result. Trace the startup and terminal error paths, then add or update the relevant tests if present. Done means runtime setup failures are handled without aborting the process and node errors such as NoReachablePeers remain visible instead of becoming NodeStopped.

Written by the indexing model from the issue text.