Avatar Selection UI Improvements for Light Mode

[XredaX]

I recently noticed and resolved several UI issues with the avatar selection interface in light mode.

Issues identified:

- Poor contrast between avatar cards and the light background
- Unnatural, box-like shadow effects instead of smooth, rounded ones
- Navigation controls (buttons and pagination dots) with insufficient visibility
- Background blur effects that looked inconsistent in light mode

Solution implemented:

I've made improvements to enhance the light mode experience while preserving the dark mode appearance:
- Added better contrast for card backgrounds
- Implemented natural-looking radial shadows using filter: drop-shadow()
- Improved visibility of navigation controls with proper styling
- Enhanced blur effects and glow transitions

Before :

After :

These changes provide a more consistent user experience across both light and dark themes.
You can see the implementation in PR #59