feat(presenter): add browser TTS (Web Speech API) + fix German umlauts

- Integrate Web Speech API into usePresenterMode for text-to-speech
- Speech-driven paragraph advancement (falls back to timer if TTS unavailable)
- TTS toggle button (Volume2/VolumeX) in PresenterOverlay
- Chrome keepAlive workaround for long speeches
- Voice selection: prefers premium/neural voices, falls back to any matching lang
- Fix all German umlauts across presenter-script, presenter-faq, i18n, route.ts

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

pitch-deck/components/PitchDeck.tsx

@@ -209,6 +209,10 @@ export default function PitchDeck({ lang, onToggleLanguage }: PitchDeckProps) {
         onResume={presenter.resume}
         onStop={presenter.stop}
         onSkip={presenter.skipSlide}
+        isSpeaking={presenter.isSpeaking}
+        ttsAvailable={presenter.ttsAvailable}
+        ttsEnabled={presenter.ttsEnabled}
+        onToggleTts={() => presenter.setTtsEnabled(!presenter.ttsEnabled)}
       />
 
       <AnimatePresence>