feat: XTTS v2 integration, auto-update system, TTS engine abstraction

- XTTS v2: Docker setup for Gaming-PC (GPU), bridge via RVS relay
- XTTS: Voice cloning UI in Diagnostic (multi-file upload)
- XTTS: Engine selectable (Piper local vs XTTS remote) with fallback
- Auto-Update: RVS serves APK over WebSocket (no HTTP needed)
- Auto-Update: App checks version on start, prompts install
- Auto-Update: release.sh copies APK to RVS via scp
- Bridge: TTS engine abstraction (piper/xtts), config persistent
- Bridge: xtts_response handler, tts_request on-demand
- Diagnostic: TTS engine dropdown, XTTS voice panel, voice cloning
- App: Play button on ARIA messages, chat search, update service
- Wake word: Disabled LiveAudioStream (crash fix), Phase 1 placeholder
- Watchdog: Container restart after 8min stuck
- Chat backup: on-the-fly to /shared/config/chat_backup.jsonl

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

.gitignore

@@ -36,6 +36,7 @@ android/local.properties
 android/package-lock.json
 *.apk
 *.aab
+rvs/updates/*.apk
 
 # ── Tauri / Desktop Build ───────────────────────
 desktop/src-tauri/target/