browser-extension project: Fix calculateColor Function Declaration

[Joaquimdacosta1999]

The calculateColor function is assigned to a variable without a proper function declaration (function calculateColor or const calculateColor = async function), which could lead to hoisting issues or confusion in strict mode. Refactor it to use a consistent declaration(e.g., const calculateColor = async (value) => {...})and ensure it’s defined before use to improve code clarity and maintainability.