optimize the appicon of iOS

ios/OralTrainer/Player/PlayerController.swift

@@ -93,6 +93,10 @@ final class PlayerController: ObservableObject {
         player.pause()
     }
 
+    func setVolume(_ volume: Float) {
+        player.volume = volume
+    }
+
     func togglePlayPause() {
         if player.timeControlStatus == .playing {
             pause()
@@ -135,8 +139,10 @@ final class PlayerController: ObservableObject {
             return false
         }
         let position = snapshot.positionMs
-        let target = item.sentences.reversed().first { $0.startMs < position - 250 }
-            ?? item.sentences.first
+        guard let target = item.sentences.reversed().first(where: { $0.startMs < position - 250 })
+            ?? item.sentences.first else {
+            return false
+        }
         seek(to: target.startMs)
         return true
     }
@@ -255,7 +261,7 @@ final class PlayerController: ObservableObject {
     func showTransientMessage(_ message: String) {
         transientMessage = message
         transientTask?.cancel()
-        transientTask = Task { [weak self] in
+        transientTask = Task { @MainActor [weak self] in
             try? await Task.sleep(nanoseconds: 1_500_000_000)
             guard !Task.isCancelled else {
                 return