Fix alarm sound session activation failures in background

Use .duckOthers instead of empty options when configuring the audio
session for alarm playback. The empty options created a non-mixable
session that conflicted with the background silent audio player
(which uses .mixWithOthers), causing setActive(true) to fail with
"Session activation failed" when the app was in the background.

Author: bjorkert

LoopFollow/Controllers/AlarmSound.swift

@@ -88,7 +88,7 @@ class AlarmSound {
             audioPlayer = try AVAudioPlayer(contentsOf: soundURL)
             audioPlayer!.delegate = audioPlayerDelegate
 
-            try AVAudioSession.sharedInstance().setCategory(.playback, mode: .default, options: [])
+            try AVAudioSession.sharedInstance().setCategory(.playback, mode: .default, options: .duckOthers)
             try AVAudioSession.sharedInstance().setActive(true)
 
             audioPlayer?.numberOfLoops = 0
@@ -126,7 +126,7 @@ class AlarmSound {
             audioPlayer = try AVAudioPlayer(contentsOf: soundURL)
             audioPlayer!.delegate = audioPlayerDelegate
 
-            try AVAudioSession.sharedInstance().setCategory(.playback, mode: .default, options: [])
+            try AVAudioSession.sharedInstance().setCategory(.playback, mode: .default, options: .duckOthers)
             try AVAudioSession.sharedInstance().setActive(true)
 
             // Only use numberOfLoops if we're not using delay-based repeating
@@ -184,7 +184,7 @@ class AlarmSound {
                 audioPlayer = try AVAudioPlayer(contentsOf: soundURL)
                 audioPlayer!.delegate = audioPlayerDelegate
 
-                try AVAudioSession.sharedInstance().setCategory(.playback, mode: .default, options: [])
+                try AVAudioSession.sharedInstance().setCategory(.playback, mode: .default, options: .duckOthers)
                 try AVAudioSession.sharedInstance().setActive(true)
 
                 audioPlayer!.numberOfLoops = 0
@@ -213,7 +213,7 @@ class AlarmSound {
             audioPlayer = try AVAudioPlayer(contentsOf: soundURL)
             audioPlayer!.delegate = audioPlayerDelegate
 
-            try AVAudioSession.sharedInstance().setCategory(.playback, mode: .default, options: [])
+            try AVAudioSession.sharedInstance().setCategory(.playback, mode: .default, options: .duckOthers)
             try AVAudioSession.sharedInstance().setActive(true)
 
             // Play endless loops
@@ -262,7 +262,7 @@ class AlarmSound {
 
     fileprivate static func enableAudio() {
         do {
-            try AVAudioSession.sharedInstance().setCategory(.playback, mode: .default, options: [])
+            try AVAudioSession.sharedInstance().setCategory(.playback, mode: .default, options: .duckOthers)
             try AVAudioSession.sharedInstance().setActive(true)
             LogManager.shared.log(category: .alarm, message: "Audio session configured for alarm playback")
         } catch {