iOS: fix sleep timer and AirPlay button size issues

- Fix chapter-based sleep timer not resetting when auto-advancing to next chapter (sleepTimerStartChapter now updates in handlePlaybackFinished)
- Fix AirPlay button being too large compared to other toolbar icons (constrain to 22×22)

ios/LibNovel/LibNovel/Services/AudioPlayerService.swift

@@ -400,6 +400,11 @@ final class AudioPlayerService: ObservableObject {
             audioURL = url
             status = .ready
             generationProgress = 100
+            
+            // Update sleep timer start chapter if using chapter-based timer
+            if case .chapters = sleepTimer {
+                sleepTimerStartChapter = next
+            }
 
             generationTask = Task {
                 await playURL(url)

ios/LibNovel/LibNovel/Views/Player/PlayerViews.swift

@@ -467,6 +467,7 @@ struct FullPlayerView: View {
                 HStack(spacing: 0) {
                     // AirPlay
                     AirPlayButton()
+                        .frame(width: 22, height: 22)
                         .frame(maxWidth: .infinity)
                     
                     // Settings (Speed control)