[FEATURE] Horizontal terminal split

## Feature Description

Opening the Claude Code in a horizontally split terminal window.

## Use Case

Screen real estate is really preferential, so it's a good idea to support as many configurations as possible.

## Proposed Solution

`split_side` should take a 3rd option: `"bottom"` (maybe include `"top"` as 4th?), which then splits the terminal horizontally. `split_width_percentage` could be just `split_percentage` or `split_ratio`.

## Alternatives Considered

It's possible to just rotate the window after creation (screenshot included), but it would be nice to skip that manual step by making it configurable.

## Additional Context

Commencez par localiser la configuration de split_side et split_width_percentage ainsi que le point d’entrée de la création de la fenêtre de terminal dans le plugin Neovim. Suivez la manière dont le split latéral existant est appliqué, puis vérifiez qu’une option bottom ou top et un pourcentage de split produisent la disposition horizontale demandée.

Rédigé par le modèle d'indexation à partir du texte de l'issue.