Feature Request: List available models when an invalid model is specified

Question

I would like to request a feature for the Codex CLI.
When a user specifies an invalid model via the `--model` flag, it would be very helpful if the CLI could list all available valid models, similar to how `cursor-agent` behaves.

**Example of desired behavior:**
```
❯ codex --model test
Cannot use this model: test. Available models: model-a, model-b, model-c...
```

This improves discoverability and user experience.