Local Countdown Timer

Local Countdown Timer: Set a browser countdown.

A simple, local countdown timer accessible from the extension's popup. Users can input a duration (minutes/seconds), and the timer runs within the extension's background script or popup. It uses standard JavaScript `setInterval` and `clearInterval` functions. Upon completion, it can play a simple sound (bundled locally with the extension) or show a browser notification (`chrome.notifications.create`) without needing any internet connection.