Leave all servers in parallel on shutdown

Quitting tells every server goodbye at once, so leaving takes as long as
the slowest server rather than all of them together. Desktop and Android
both go through ServerSession.shutdownAll.

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

android/app/src/main/java/com/ts3client/android/ServerController.kt

@@ -117,11 +117,10 @@ class ServerController internal constructor(
         session.disconnect()
     }
 
-    /** Leaves the server before returning, for when the app goes away with the connection. */
-    internal fun leave() {
+    /** Before the app goes away with the connection, which [SessionController.leave] then ends. */
+    internal fun leaving() {
         left = true
         network.leaving()
-        session.shutdown()
     }
 
     internal fun dispose() {

android/app/src/main/java/com/ts3client/android/SessionController.kt

@@ -21,6 +21,7 @@ import com.ts3client.myts.MyTeamSpeak
 import com.ts3client.net.HostButton
 import com.ts3client.myts.MyTeamSpeakLogin
 import com.ts3client.session.SelfState
+import com.ts3client.session.ServerSession
 import com.ts3client.session.Sessions
 import com.ts3client.sound.SoundNotifier
 import com.ts3client.sound.SoundPack
@@ -199,7 +200,9 @@ class SessionController(private val context: Context) {
 
     /** Leaves every server before returning, for when the app goes away with the connections. */
     fun leave() {
-        _servers.value.forEach(ServerController::leave)
+        val servers = _servers.value
+        servers.forEach(ServerController::leaving)
+        ServerSession.shutdownAll(servers.map { it.session })
         contactStore.flush()
     }