[Feature]: Show argument hints when no more subcommands available #127

Is your feature request related to a problem?

When pressing tab on a leaf command, nothing is suggested if the user hasn't typed a flag prefix. There is no indication of what argument is expected next.

Describe the solution you'd like

When tab-completing a command that has no subcommands (a leaf command), and the user hasn't started typing a flag (-), the completion should display the next expected positional argument as a hint (e.g. ).

If the command has registered arguments and the user is at the position of the next argument, the completion should display the argument placeholder as a hint e.g.:
command subcommand <TAB>
<argument> -- Description of the argument

Describe alternatives you've considered

No response

Additional context

No response

AI assistance disclosure

• This feature request was drafted with the assistance of an AI tool.