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/android/app/src/main/java/com/ariacockpit/PcmStreamPlayerModule.kt

@@ -30,9 +30,10 @@ import java.util.concurrent.LinkedBlockingQueue
 class PcmStreamPlayerModule(reactContext: ReactApplicationContext) : ReactContextBaseJavaModule(reactContext) {
     companion object {
         private const val TAG = "PcmStreamPlayer"
-        // Sekunden Audio die VOR play()-Start gepuffert sein muessen.
-        // 2.5s Vorrat = genug um XTTS-Render-Pausen zwischen Chunks zu puffern.
-        private const val PREROLL_SECONDS = 2.5
+        // Fallback wenn JS keinen Wert uebergibt.
+        private const val DEFAULT_PREROLL_SECONDS = 3.5
+        private const val MIN_PREROLL_SECONDS = 0.5
+        private const val MAX_PREROLL_SECONDS = 10.0
         // Stille am Stream-Anfang, damit AudioTrack sauber anfaehrt und die
         // ersten Samples nicht abgeschnitten werden (XTTS-Warmup + play()-Latenz).
         private const val LEADING_SILENCE_SECONDS = 0.2
@@ -53,17 +54,21 @@ class PcmStreamPlayerModule(reactContext: ReactApplicationContext) : ReactContex
     // ── Lifecycle ──
 
     @ReactMethod
-    fun start(sampleRate: Int, channels: Int, promise: Promise) {
+    fun start(sampleRate: Int, channels: Int, prerollSeconds: Double, promise: Promise) {
         try {
             // Alte Session beenden falls vorhanden
             stopInternal()
 
+            val prerollSec = prerollSeconds
+                .coerceIn(MIN_PREROLL_SECONDS, MAX_PREROLL_SECONDS)
+                .let { if (it.isFinite() && it > 0) it else DEFAULT_PREROLL_SECONDS }
+
             val channelConfig = if (channels == 2) AudioFormat.CHANNEL_OUT_STEREO else AudioFormat.CHANNEL_OUT_MONO
             val encoding = AudioFormat.ENCODING_PCM_16BIT
             val minBuf = AudioTrack.getMinBufferSize(sampleRate, channelConfig, encoding)
             val bytesPerSecond = sampleRate * channels * 2 // 16-bit = 2 bytes
             // Buffer muss mindestens PREROLL + etwas Spielraum fassen.
-            val prerollTarget = (bytesPerSecond * PREROLL_SECONDS).toInt()
+            val prerollTarget = (bytesPerSecond * prerollSec).toInt()
             val bufferSize = (minBuf * 32).coerceAtLeast(prerollTarget * 2)
             prerollBytes = prerollTarget
             bytesBuffered = 0
@@ -173,7 +178,7 @@ class PcmStreamPlayerModule(reactContext: ReactApplicationContext) : ReactContex
                 }
             }, "PcmStreamWriter").apply { start() }
 
-            Log.i(TAG, "Stream gestartet: ${sampleRate}Hz ch=$channels buf=${bufferSize}B preroll=${prerollBytes}B")
+            Log.i(TAG, "Stream gestartet: ${sampleRate}Hz ch=$channels buf=${bufferSize}B preroll=${prerollBytes}B (${prerollSec}s)")
             promise.resolve(true)
         } catch (e: Exception) {
             Log.e(TAG, "start fehlgeschlagen", e)