Validation errors identify an argument by its numeric position

[HafizMMoaz]

Argument definitions are keyed by position and have no name, so validateDefinitions() puts the raw index into the message (src/Command.php:359):

protected array $argumentDefinitions = [
    0 => ["type" => "string", "required" => true],
];

php app deploy
# argument "0" is required.

The user has no way to know what argument 0 is meant to be, and the generated help does not print the definitions either (#49), so there is nowhere to look it up.

Suggested fix: let a definition carry a name (and ideally a description), fall back to the position when it is absent, and use the name in the message:

argument "environment" is required.

The same name then feeds the Usage: and Arguments: blocks in #49, so a command declares each input once instead of describing it in $usage by hand.