Rebuilt the cleaning engine on declarativeNetRequest: playlist/mix context is now stripped from the request before YouTube loads, so the page never enters a Mix and there is no reload or flash (Chrome). Replaces the previous approach that only edited the address bar after the Mix had already loaded.

Added a content-script fallback for in-app navigations (clicking a Mix while already on YouTube) and for browsers without declarativeNetRequest; it cleans via location.replace, so the Back button always returns to the previous page rather than the playlist.

Reworked the popup into a master switch plus independent "Mixes & radio" and "Playlists" toggles, so cleaning can be limited to either type or turned off entirely.

Useful watch parameters (such as the t timestamp) are preserved while playlist context is removed.
Permissions: added storage and declarativeNetRequestWithHostAccess (neither shows an install warning) and removed the now-unused tabs permission (the background watcher that relied on it was replaced by the declarativeNetRequest engine), so existing users update without having to re-enable the extension.