fix(android): fully close the app on swipe-away and avoid duplicate cookie DataStore

Initialize NewPipeDownloader once per process so recreating the Activity
no longer opens a second DataStore on spotube_cookies.preferences_pb.
Kill the process after PlaybackService shuts down on task removal so the
proxy server, MQTT client and singletons don't linger in the background.

composeApp/src/androidJvmMain/kotlin/org/spotube/spotube/core/newpipe/NewPipeDownloader.kt

@@ -82,10 +82,16 @@ class NewPipeDownloader(private val cookieJar: PersistentCookieJar) : Downloader
     companion object {
         private var instance: NewPipeDownloader? = null
 
+            /**
+         * Safe to call on every Activity creation: the process (and so this singleton) outlives
+         * the Activity, and a second [PersistentCookieJar] would open a second DataStore on the
+         * same cookies file, which DataStore rejects.
+         */
+        @Synchronized
         fun init(paths: Paths) {
+            if (instance != null) return
             val cookieJar = PersistentCookieJar(paths)
-            instance = NewPipeDownloader(cookieJar)
+            instance = NewPipeDownloader(cookieJar).also { NewPipe.init(it) }
-            NewPipe.init(instance)
         }
     }
 }

composeApp/src/androidMain/kotlin/org/spotube/spotube/media/PlaybackService.kt

@@ -23,6 +23,7 @@ import android.app.NotificationManager
 import android.app.PendingIntent
 import android.content.Intent
 import android.os.Build
+import android.os.Process
 import android.util.Log
 import androidx.annotation.OptIn
 import androidx.core.app.NotificationCompat
@@ -61,6 +62,8 @@ import spotube.composeapp.generated.resources.notification_playback_channel_name
 
 @OptIn(UnstableApi::class)
 class PlaybackService : MediaLibraryService(), KoinComponent {
+    private var taskRemoved = false
+
 
     private val audioPlayer = inject<AudioPlayerInterface>().value as AudioPlayer
     private val audioPlayerQueue: AudioPlayerQueue by inject()
@@ -161,9 +164,13 @@ class PlaybackService : MediaLibraryService(), KoinComponent {
         removeSession(librarySession)
         librarySession.release()
         super.onDestroy()
+        // Swiping the app out of recents should fully close it: Android otherwise keeps this
+        // process cached with the proxy server, MQTT client and every singleton still alive.
+        if (taskRemoved) Process.killProcess(Process.myPid())
     }
 
     override fun onTaskRemoved(rootIntent: Intent?) {
+        taskRemoved = true
         pauseAllPlayersAndStopSelf()
     }