Feature Request: Fullscreen and Centered Board Layout

[wonderkid894]

Hi! First of all, thank you for this amazing project — En Croissant is by far the best chess GUI I've found on Linux.

I'd love to suggest a layout improvement: a fullscreen board mode, similar to what CoreChess offers. The idea is to allow the user to focus entirely on the board, without side panels or distractions — ideal for playing or reviewing games in a clean, immersive way.

Additionally, a centered board layout (instead of the current left-aligned position) would be much more comfortable for the eyes, especially on wide screens. Having the board in the middle feels more natural and balanced, and would be a great option for users who prefer minimalism.

Thanks again for your work — En Croissant is already fantastic, and this feature would make it even better!