Fix TTS audio routing for Android Auto

Set AudioAttributes (USAGE_ASSISTANT) on the TTS engine itself,
not just on the AudioFocusRequest. Without this, TTS output goes
to the phone speaker instead of routing through Android Auto's
head unit.

app/src/main/java/farm/hobbs/clippyauto/voice/TTSManager.kt

@@ -52,6 +52,8 @@ class TTSManager(
         tts = TextToSpeech(context) { status ->
             if (status == TextToSpeech.SUCCESS) {
                 tts?.language = Locale.US
+                // Route TTS audio through Android Auto head unit
+                tts?.setAudioAttributes(audioFocusRequest.audioAttributes)
                 tts?.setOnUtteranceProgressListener(object : UtteranceProgressListener() {
                     override fun onStart(utteranceId: String?) {
                         LatencyTracker.markT5() // t5: First audio frame