iOS: section reorder and visibility, CarPlay downloads fix, stem playlist refresh fix

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

ios/Stemify/Core/Settings.swift

@@ -226,6 +226,8 @@ final class Settings: @unchecked Sendable {
     /// Downloads page order: 0 download order, 1 artist, 2 release date.
     /// Library screen row order, titles joined by "|". Unlisted rows keep their default place after the listed ones.
     var libraryOrder: String { get { read(\.libraryOrder, "libraryOrder", "") } set { write(\.libraryOrder, "libraryOrder", newValue, "") } }
+    /// Library screen sections the user switched off, titles joined by "|".
+    var libraryHidden: String { get { read(\.libraryHidden, "libraryHidden", "") } set { write(\.libraryHidden, "libraryHidden", newValue, "") } }
     var downloadSort: Int { get { read(\.downloadSort, "downloadSort", 0) } set { write(\.downloadSort, "downloadSort", newValue, 0) } }
     var karaokeVocals: Int { get { read(\.karaokeVocals, "karaokeVocals", KaraokeVocals.Off.rawValue) } set { write(\.karaokeVocals, "karaokeVocals", newValue, KaraokeVocals.Off.rawValue) } }
     /// How far down Soft karaoke puts the vocals, in dB.