chore: avoid silent exit by printing server error (#3095)

printing server startup error if an error was discovered. Previously it
will just exit silently if theres an unknown flag caught by Cobra.

🛠️ Fixes #3063

---------

Co-authored-by: gemini-code-assist[bot] <176961590+gemini-code-assist[bot]@users.noreply.github.com>

Author: Yuan325

cmd/root.go

@@ -87,6 +87,7 @@ func Execute() {
 	opts := internal.NewToolboxOptions()
 
 	if err := NewCommand(opts).Execute(); err != nil {
+		fmt.Fprintf(opts.IOStreams.ErrOut, "Error: %v\n", err)
 		exit := 1
 		os.Exit(exit)
 	}