feat: Modernize group screens UI

Redesigned the group list and group details screens with a modern and bold UI.

- Introduced a new color palette and typography theme for consistency.
- Updated the layout of the group list and group details screens to be more intuitive and visually appealing.
- Added animations and transitions to improve the user experience.
- The new design is inspired by modern aesthetics to appeal to a younger audience.

Author: google-labs-jules[bot]