Add WCAG Contrast Checker Utility

[joaogsribeiro]

Description

This PR adds a new utility: WCAG Contrast Checker.

It helps developers and designers ensure their color combinations meet accessibility standards (AA/AAA) based on official W3C formulas.

This project evolved from a simple color picker to a full accessibility tool, and finally to a Browser Extension (Manifest V3) with EyeDropper API support.

Linked Issue

Closes #443

Features

• [x] Real-time contrast ratio calculation (W3C relative luminance).
• [x] Dynamic preview box.
• [x] EyeDropper API integration (Pick color from screen).
• [x] Manual input support (HEX/RGB).
• [x] Logic kept under 100 lines of JS (96 lines).
• [x] Chrome Extension support (Manifest V3).

Tech Stack

• HTML5, CSS3 (Flexbox/Grid), Vanilla JavaScript.

Thank you!