Spoken directions can go over the music channel

A 2025 Nissan's Bosch unit drops the link a second after every turn
on its directions channel while its music channel is open, and it
plays music through nothing else (#35). A new car setting, off by
default, leaves the directions channel alone: each turn is mixed into
the music with the music turned down under it, or, when nothing is
playing, goes out on the music channel on its own under ducking focus.

gearslip/src/main/java/app/seb3thehacker/gearslip/car/CarSettingsScreen.kt

@@ -67,6 +67,7 @@ fun CarSettingsScreen() {
     val whatsNew by CarSettings.whatsNewAfterUpdates.collectAsState()
     val pipeAudio by CarSettings.pipeAudio.collectAsState()
     val speakDirections by CarSettings.speakDirections.collectAsState()
+    val directionsOverMusic by CarSettings.directionsOverMusic.collectAsState()
     val bluetoothWarning by CarSettings.bluetoothWarning.collectAsState()
     val locationWarning by CarSettings.locationWarning.collectAsState()
     val autoplay by CarSettings.autoplay.collectAsState()
@@ -287,6 +288,22 @@ fun CarSettingsScreen() {
                 )
             }
 
+            if (section == chosen && speakDirections) item {
+                ChoiceRow(
+                    stringResource(R.string.car_directions_over_music),
+                    listOf(false to stringResource(R.string.off), true to stringResource(R.string.on)),
+                    directionsOverMusic,
+                ) { CarSettings.setDirectionsOverMusic(it) }
+            }
+
+            if (section == chosen && speakDirections) item {
+                Text(
+                    stringResource(R.string.car_directions_over_music_note),
+                    style = MaterialTheme.typography.bodySmall,
+                    color = MaterialTheme.colorScheme.onSurfaceVariant,
+                )
+            }
+
             if (section == chosen) item {
                 ExperimentalFeatureRow(
                     title = stringResource(R.string.car_phone_speech),