fix: respect Hidden flag for help command in usage output

[ricardbejarano]

Summary

Fixes #2269

The help command was hardcoded to always appear in usage listings, completely ignoring its Hidden field. This meant that setting cmd.Hidden = true on the help command had no effect, making the property meaningless for it.

What changed

Updated all locations where the help command receives special treatment to check !subcmd.Hidden before including it in output:

• defaultUsageTemplate: template conditions updated from (eq .Name "help") to (and (eq .Name "help") (not .Hidden))
• printOptionCmdUsages: three loop conditions updated
• AllChildCommandsHaveGroup: condition updated to respect Hidden
• Shell completion listing: condition updated to respect Hidden

How to hide the help command

rootCmd.InitDefaultHelpCmd()
rootCmd.helpCommand.Hidden = true

Or via SetHelpCommand:

rootCmd.SetHelpCommand(&cobra.Command{Hidden: true})

Testing

Added TestHiddenHelpCommandIsHidden which verifies the help command appears in usage by default and disappears when Hidden is set to true.

All existing tests pass.

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