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>

diagnostic/server.js

@@ -1173,6 +1173,8 @@ wss.on("connection", (ws) => {
           defaultVoice: msg.defaultVoice || "ramona",
           highlightVoice: msg.highlightVoice || "thorsten",
           ttsEnabled: msg.ttsEnabled !== false,
+          ttsEngine: msg.ttsEngine || "piper",
+          xttsVoice: msg.xttsVoice || "",
           speedRamona: msg.speedRamona || 1.0,
           speedThorsten: msg.speedThorsten || 1.0,
         };