Add an ns1 test-and-deploy workflow for the Go MCP server.

scripts/deploy-138.sh tests with Go 1.26.9, swaps the live binary, and rolls back if port 8000 stops answering. Port 0 in the embedded NATS listener now picks an ephemeral port so the test can run while 4222 is already taken.

internal/embednats/server.go

@@ -119,5 +119,15 @@ func splitHostPort(listen string) (string, int, error) {
 	if host == "" {
 		host = "127.0.0.1"
 	}
+	// nats-server treats port 0 as its default (4222), which is already taken
+	// on ns1. Bind an ephemeral port and hand that number to the server.
+	if port == 0 {
+		ln, err := net.Listen("tcp", net.JoinHostPort(host, "0"))
+		if err != nil {
+			return "", 0, fmt.Errorf("embednats: ephemeral listen: %w", err)
+		}
+		port = ln.Addr().(*net.TCPAddr).Port
+		ln.Close()
+	}
 	return host, port, nil
 }