feat: initial project scaffold

- Android Auto CarAppService, Session, Screen
- Voice pipeline: STT (SpeechManager), TTS (TTSManager), VoiceStateMachine
- Matrix REST client (login, send, sync) - no E2EE, raw API
- FCM push receiver with response dedup
- Network monitor + offline message queue
- Phone setup activity stub
- Full architecture spec in docs/ARCHITECTURE.md

build.gradle.kts

@@ -0,0 +1,5 @@
+plugins {
+    id("com.android.application") version "8.7.3" apply false
+    id("org.jetbrains.kotlin.android") version "2.1.10" apply false
+    id("com.google.gms.google-services") version "4.4.2" apply false
+}