Feat: setting to auto-translate lyrics for all songs by default

## Request Add a toggle in Settings > Lyrics to auto-translate every song's lyrics to the user's preferred language on load — no per-song manual trigger needed. ## Use case Users who always listen to foreign-language music (e.g. K-pop, J-pop) want translation on by default without tapping "translate" each time. ## Behaviour - Setting off (default): current behaviour, translate on demand - Setting on: translation runs automatically when lyrics load Related: #4083 (provider options), #3652 (re-translate button)