feat: Pre-Roll-Buffer fuer TTS einstellbar in App-Settings

- Kotlin start() nimmt jetzt prerollSeconds als dritten Parameter
  (1.0-6.0s geclampt, Fallback 3.5s bei ungueltigem Wert)
- audio.ts liest Wert aus AsyncStorage vor jedem Stream-Start,
  exportiert Default/Min/Max/Key als Konstanten
- SettingsScreen: +/- Buttons direkt unter dem TTS-Toggle,
  Default auf 3.5s (von 2.5s) angehoben

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

android/src/screens/SettingsScreen.tsx

@@ -20,6 +20,12 @@ import AsyncStorage from '@react-native-async-storage/async-storage';
 import RNFS from 'react-native-fs';
 import DocumentPicker from 'react-native-document-picker';
 import rvs, { ConnectionState, RVSMessage, ConnectionConfig, ConnectionLogEntry } from '../services/rvs';
+import {
+  TTS_PREROLL_DEFAULT_SEC,
+  TTS_PREROLL_MIN_SEC,
+  TTS_PREROLL_MAX_SEC,
+  TTS_PREROLL_STORAGE_KEY,
+} from '../services/audio';
 import ModeSelector from '../components/ModeSelector';
 import QRScanner from '../components/QRScanner';
 import VoiceCloneModal from '../components/VoiceCloneModal';
@@ -73,6 +79,7 @@ const SettingsScreen: React.FC = () => {
   const [autoDownload, setAutoDownload] = useState(true);
   const [storageSize, setStorageSize] = useState('...');
   const [ttsEnabled, setTtsEnabled] = useState(true);
+  const [ttsPrerollSec, setTtsPrerollSec] = useState<number>(TTS_PREROLL_DEFAULT_SEC);
   const [editingPath, setEditingPath] = useState(false);
   const [xttsVoice, setXttsVoice] = useState('');
   const [availableVoices, setAvailableVoices] = useState<Array<{name: string, size: number}>>([]);
@@ -99,6 +106,14 @@ const SettingsScreen: React.FC = () => {
     AsyncStorage.getItem('aria_tts_enabled').then(saved => {
       if (saved !== null) setTtsEnabled(saved === 'true');
     });
+    AsyncStorage.getItem(TTS_PREROLL_STORAGE_KEY).then(saved => {
+      if (saved != null) {
+        const n = parseFloat(saved);
+        if (isFinite(n) && n >= TTS_PREROLL_MIN_SEC && n <= TTS_PREROLL_MAX_SEC) {
+          setTtsPrerollSec(n);
+        }
+      }
+    });
     AsyncStorage.getItem('aria_xtts_voice').then(saved => {
       if (saved) setXttsVoice(saved);
     });
@@ -527,6 +542,42 @@ const SettingsScreen: React.FC = () => {
           />
         </View>
 
+        {ttsEnabled && (
+          <View style={{marginTop: 20}}>
+            <Text style={styles.toggleLabel}>Puffer vor Wiedergabestart</Text>
+            <Text style={styles.toggleHint}>
+              Wie viel Audio gesammelt wird bevor die Wiedergabe startet.
+              Hoeher = robuster gegen Render-Pausen, aber mehr Startverzoegerung.
+              Default: {TTS_PREROLL_DEFAULT_SEC.toFixed(1)}s.
+            </Text>
+            <View style={styles.prerollRow}>
+              <TouchableOpacity
+                style={styles.prerollButton}
+                onPress={() => {
+                  const next = Math.max(TTS_PREROLL_MIN_SEC, Math.round((ttsPrerollSec - 0.5) * 10) / 10);
+                  setTtsPrerollSec(next);
+                  AsyncStorage.setItem(TTS_PREROLL_STORAGE_KEY, String(next));
+                }}
+                disabled={ttsPrerollSec <= TTS_PREROLL_MIN_SEC}
+              >
+                <Text style={styles.prerollButtonText}>−0.5</Text>
+              </TouchableOpacity>
+              <Text style={styles.prerollValue}>{ttsPrerollSec.toFixed(1)} s</Text>
+              <TouchableOpacity
+                style={styles.prerollButton}
+                onPress={() => {
+                  const next = Math.min(TTS_PREROLL_MAX_SEC, Math.round((ttsPrerollSec + 0.5) * 10) / 10);
+                  setTtsPrerollSec(next);
+                  AsyncStorage.setItem(TTS_PREROLL_STORAGE_KEY, String(next));
+                }}
+                disabled={ttsPrerollSec >= TTS_PREROLL_MAX_SEC}
+              >
+                <Text style={styles.prerollButtonText}>+0.5</Text>
+              </TouchableOpacity>
+            </View>
+          </View>
+        )}
+
         {ttsEnabled && (
           <View style={{marginTop: 20}}>
             <Text style={styles.toggleLabel}>Stimme (geraetelokal)</Text>
@@ -1118,6 +1169,34 @@ const styles = StyleSheet.create({
   bottomSpacer: {
     height: 40,
   },
+
+  prerollRow: {
+    flexDirection: 'row',
+    alignItems: 'center',
+    justifyContent: 'center',
+    marginTop: 12,
+    gap: 16,
+  },
+  prerollButton: {
+    backgroundColor: '#2A2A3E',
+    paddingHorizontal: 18,
+    paddingVertical: 10,
+    borderRadius: 8,
+    minWidth: 72,
+    alignItems: 'center',
+  },
+  prerollButtonText: {
+    color: '#FFFFFF',
+    fontSize: 16,
+    fontWeight: '600',
+  },
+  prerollValue: {
+    color: '#FFFFFF',
+    fontSize: 20,
+    fontWeight: '700',
+    minWidth: 80,
+    textAlign: 'center',
+  },
 });
 
 export default SettingsScreen;