fix: hide GLOBAL OPTIONS in completion command help

The completion command ignores global flags by design, so displaying
them in --help output is misleading. Return nil from
VisiblePersistentFlags() when isCompletionCommand is true.

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

Author: suzuki-shunsuke

command.go

@@ -303,6 +303,9 @@ func (cmd *Command) appendFlag(fl Flag) {
 
 // VisiblePersistentFlags returns a slice of [LocalFlag] with Persistent=true and Hidden=false.
 func (cmd *Command) VisiblePersistentFlags() []Flag {
+	if cmd.isCompletionCommand {
+		return nil
+	}
 	var flags []Flag
 	for _, fl := range cmd.Root().Flags {
 		pfl, ok := fl.(LocalFlag)

completion_test.go

@@ -52,6 +52,7 @@ func TestCompletionHelp(t *testing.T) {
 
 			r.NoError(cmd.Run(buildTestContext(t), test.args))
 			r.Contains(out.String(), "USAGE")
+			r.NotContains(out.String(), "GLOBAL OPTIONS")
 		})
 	}
 }