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

.gitignore

@@ -0,0 +1,13 @@
+*.iml
+.gradle
+/local.properties
+/.idea
+.DS_Store
+/build
+/captures
+.externalNativeBuild
+.cxx
+local.properties
+google-services.json
+*.apk
+*.aab