fix: return a cleanup function from PopupPage's useEffect hook

[nicomiguelino]

Issues Fixed

Up[dated PopupPage's useEffect hook to return a function that cleans up event listeners on component unmount.

Description

A Copilot review comment in #108 says that the event listener added in the useEffect hook of the PopupPage component is not removed on component unmount.

Checklist

• I have performed a self-review of my own code.
• New and existing unit tests pass locally and on CI with my changes.
• I have tested my changes on Google Chrome.
• I have tested my changes on Mozilla Firefox.
• I added a documentation for the changes I have made (when necessary).

PR Overview

This PR fixes the event listener cleanup issue in PopupPage by refactoring the useEffect hook.

• Extracts the event listener callback into a named constant.
• Adds a cleanup function to remove the event listener on component unmount.

Reviewed Changes

File	Description
src/assets/ts/popup.tsx	Refactored useEffect hook to attach and clean up the event listener

Copilot reviewed 1 out of 1 changed files in this pull request and generated no comments.