Add a theme switcher

**Describe the solution you'd like**
Add a theme switcher similar to [Channel Surfers](https://channel-surfers.com). Themes should be [those made by shadcn](https://ui.shadcn.com/themes) (we can add more later)

The theme should also live update as you hover over each item in the list

Start by locating the frontend entry point for the list and its current styling or theme handling. Review the Channel Surfers and shadcn themes references, then implement a switcher for the listed themes with live updates while hovering each list item; done means both behaviors work consistently in the application.

Written by the indexing model from the issue text.