Migrate Root Command from urfave to Cobra + Fang
mainReplace the legacy seshcli/seshcli.go logic with a new Cobra root command structure. Instead of using app.Run(), use fang.Execute() to run the command tree.
// Before (urfave)
app := seshcli.App(version)
app.Run(os.Args)
// After (Cobra + Fang)
cmd := seshcli.NewRootCommand(version)
fang.Execute(context.TODO(), cmd)