Fix behavior of back button when adding additional accounts

feature/launcher/src/main/kotlin/app/k9mail/feature/launcher/navigation/FeatureLauncherNavHost.kt

@@ -16,6 +16,7 @@ import org.koin.compose.koinInject
 fun FeatureLauncherNavHost(
     navController: NavHostController,
     startDestination: String?,
+    onBack: () -> Unit,
     modifier: Modifier = Modifier,
     importSettingsLauncher: ImportSettingsLauncher = koinInject(),
     accountSetupFinishedLauncher: AccountSetupFinishedLauncher = koinInject(),
@@ -30,7 +31,7 @@ fun FeatureLauncherNavHost(
             onImport = { importSettingsLauncher.launch() },
         )
         accountSetupRoute(
-            onBack = navController::popBackStack,
+            onBack = onBack,
             onFinish = { accountSetupFinishedLauncher.launch(it) },
         )
     }

feature/launcher/src/main/kotlin/app/k9mail/feature/launcher/ui/FeatureLauncherApp.kt

@@ -5,6 +5,7 @@ import androidx.compose.foundation.layout.safeDrawingPadding
 import androidx.compose.runtime.Composable
 import androidx.compose.ui.Modifier
 import androidx.navigation.compose.rememberNavController
+import app.k9mail.core.ui.compose.common.activity.LocalActivity
 import app.k9mail.core.ui.compose.designsystem.atom.Background
 import app.k9mail.core.ui.compose.theme.K9Theme
 import app.k9mail.feature.launcher.navigation.FeatureLauncherNavHost
@@ -23,9 +24,12 @@ fun FeatureLauncherApp(
                 .safeDrawingPadding()
                 .then(modifier),
         ) {
+            val activity = LocalActivity.current
+
             FeatureLauncherNavHost(
                 navController = navController,
                 startDestination = startDestination,
+                onBack = { activity.finish() },
             )
         }
     }