Support Ctrl+N / Ctrl+P for list navigation

### Summary

When navigating stacks and prompts, only the arrow keys work for moving the selection up and down. Ctrl+N / Ctrl+P do not work as alternatives.

### Expected behavior

Support Unix / editor-style navigation so that:

- `Ctrl+N` moves to the next item (down)
- `Ctrl+P` moves to the previous item (up)

This matches common behavior in Vim, Emacs, VS Code, and many terminal UIs, and lets users keep their hands on the home row while working with `gh stack`.

> Optionally, supporting `Ctrl+J` / `Ctrl+K` for down/up (or allowing these to be configured) would make the experience even more familiar for Vim users.

### Actual behavior

Arrow keys move the selection, but `Ctrl+N` / `Ctrl+P` have no effect.

### Environment

- `gh` version: 2.90.0
- `gh stack` version: 0.0.2

Comece pelos pontos de entrada de navegação de stack e prompt da gh stack CLI, rastreando onde o movimento da seleção pelas teclas de seta é tratado. Adicione a navegação com Ctrl+N e Ctrl+P com a mesma direção e o mesmo comportamento das teclas de seta e, em seguida, verifique se ambos os bindings movem a seleção corretamente.

Escrita pelo modelo de indexação a partir do texto da issue.