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/services/audio.ts

@@ -9,6 +9,7 @@
 import { Platform, PermissionsAndroid, NativeModules } from 'react-native';
 import Sound from 'react-native-sound';
 import RNFS from 'react-native-fs';
+import AsyncStorage from '@react-native-async-storage/async-storage';
 import AudioRecorderPlayer, {
   AudioEncoderAndroidType,
   AudioSourceAndroidType,
@@ -41,7 +42,7 @@ const { AudioFocus, PcmStreamPlayer } = NativeModules as {
     release: () => Promise<boolean>;
   };
   PcmStreamPlayer?: {
-    start: (sampleRate: number, channels: number) => Promise<boolean>;
+    start: (sampleRate: number, channels: number, prerollSeconds: number) => Promise<boolean>;
     writeChunk: (base64Pcm: string) => Promise<boolean>;
     end: () => Promise<boolean>;
     stop: () => Promise<boolean>;
@@ -80,6 +81,26 @@ const VAD_SPEECH_MIN_MS = 500;         // ms Sprache bevor Aufnahme zaehlt — l
 // Max-Dauer einer Aufnahme in Gespraechsmodus (Notbremse gegen Runaway-Loops)
 const MAX_RECORDING_MS = 30000;
 
+// Pre-Roll: Wie lange Audio im AudioTrack-Buffer liegt bevor play() startet.
+// Einstellbar via Diagnostic/Settings (Key: aria_tts_preroll_sec).
+export const TTS_PREROLL_DEFAULT_SEC = 3.5;
+export const TTS_PREROLL_MIN_SEC = 1.0;
+export const TTS_PREROLL_MAX_SEC = 6.0;
+export const TTS_PREROLL_STORAGE_KEY = 'aria_tts_preroll_sec';
+
+async function loadPrerollSec(): Promise<number> {
+  try {
+    const raw = await AsyncStorage.getItem(TTS_PREROLL_STORAGE_KEY);
+    if (raw != null) {
+      const n = parseFloat(raw);
+      if (isFinite(n) && n >= TTS_PREROLL_MIN_SEC && n <= TTS_PREROLL_MAX_SEC) {
+        return n;
+      }
+    }
+  } catch {}
+  return TTS_PREROLL_DEFAULT_SEC;
+}
+
 // --- Audio-Service ---
 
 class AudioService {
@@ -373,8 +394,9 @@ class AudioService {
       this.pcmBuffer = [];
       this.pcmBytesCollected = 0;
       if (!silent) {
+        const prerollSec = await loadPrerollSec();
         try {
-          await PcmStreamPlayer!.start(sampleRate, channels);
+          await PcmStreamPlayer!.start(sampleRate, channels, prerollSec);
         } catch (err) {
           console.error('[Audio] PcmStreamPlayer.start fehlgeschlagen:', err);
           this.pcmStreamActive = false;