`mix igniter.new` doesn't support `--help` directly.

**Describe the bug**
I keep typing `mix igniter.new --help` looking for a list of available options, except I get the following error:

```
Required positional argument missing: project_name.

Usage:

mix igniter.new project_name [options]
```

**To Reproduce**
```
$ mix igniter.new --help
```

**Expected behavior**

It should output the same output as `mix help igniter.new`.

** Runtime

- Elixir version 1.18.1
- Erlang version 27.2
- OS macOS Sequoia 15.2 (24C101)
- Igniter version `0.5.6`
- any related extension versions

Start by running `mix igniter.new --help` and compare its behavior with `mix help igniter.new`. Trace the `mix igniter.new` command entry point and make the direct help invocation produce the same help output without requiring `project_name`; confirm the reproduction command and existing help command both behave as expected.

Written by the indexing model from the issue text.