Replace inconsistent icons with an icon library

Our current icons are not consistent. They differ in style, stroke width, size, and visual weight, which makes the UI feel less polished and cohesive. They come from different sources, so there's no unified look.

Suggested solution: Replace all icons with a single, well-maintained icon library such as [Lucide](https://lucide.dev/), [Tabler Icons](https://tabler.io/icons), or [Phosphor Icons](https://phosphoricons.com/) to ensure a consistent style across the project.