Document why Service binds to gateway IP only

Explain in the Service struct doc that only the gateway IP is reachable
from the guest, and point callers to Provider.VirtualNetwork().Listen
for custom addresses.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: JAORMX

net/hosted/service.go

@@ -15,10 +15,14 @@ import (
 )
 
 // Service describes an HTTP service to expose inside the virtual network.
-// The service listens on the gateway IP (192.168.127.1) at the given port,
-// making it reachable from the guest VM without opening a real host socket.
+//
+// Services always bind to the gateway IP ([topology.GatewayIP], 192.168.127.1)
+// because that is the only host-side address reachable from the guest. Callers
+// that need to listen on a different address can use
+// [Provider.VirtualNetwork].Listen directly.
 type Service struct {
-	// Port is the TCP port to listen on inside the virtual network.
+	// Port is the TCP port to listen on at the gateway IP inside the
+	// virtual network.
 	Port uint16
 
 	// Handler is the HTTP handler that serves requests.