ax(node): replace prose comment with usage example on Transport.Send

AX Principle 2: comments that restate the type signature add zero
information. Replaced "Send sends a message to a specific peer." with a
concrete call-site example showing error handling.

Co-Authored-By: Charon <charon@lethean.io>

pkg/node/transport.go

@@ -361,7 +361,7 @@ func (t *Transport) Connect(peer *Peer) (*PeerConnection, error) {
 	return pc, nil
 }
 
-// Send sends a message to a specific peer.
+// if err := transport.Send(peer.ID, msg); err != nil { return err }
 func (t *Transport) Send(peerID string, msg *Message) error {
 	t.mu.RLock()
 	pc, exists := t.conns[peerID]