fix: Audio preloading to prevent stuttering, remove trailing dots for XTTS

- Preload next audio while current plays (eliminates gap between sentences)
- Remove trailing dots from sentences (XTTS reads them aloud)
- stopPlayback cleans up preloaded audio

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

xtts/bridge.js

@@ -101,7 +101,10 @@ async function handleTTSRequest(payload) {
   const cleanText = text.replace(/\*\*([^*]+)\*\*/g, "$1").trim();
 
   // Text in Saetze aufteilen (sequentiell rendern fuer korrekte Reihenfolge)
-  const sentences = cleanText.split(/(?<=[.!?])\s+/).map(s => s.trim()).filter(s => s.length > 0);
+  const sentences = cleanText.split(/(?<=[.!?])\s+/)
+    .map(s => s.trim())
+    .filter(s => s.length > 0)
+    .map(s => s.replace(/[.]+$/, '')); // Punkt am Ende entfernen (XTTS liest ihn sonst vor)
   if (sentences.length === 0) return;
 
   log(`TTS-Request: "${cleanText.slice(0, 60)}..." (${sentences.length} Saetze, voice: ${voice || "default"}, lang: ${language || "de"})`);