This change makes the browser action icon flash to a light variant on successful Last.fm calls and a dark variant when scrobble or updateNowPlaying requests fail, instead of silently logging results to the console. It also factors XML response validation into shared logic for auth and request handling, then wires the background script to reset the icon back to default after a short delay. The docs and usage page were updated to explain the new behavior, so users now get quick feedback on whether a scrobble actually worked.