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/ChatFAB.tsx

@@ -324,7 +324,7 @@ export default function ChatFAB({
               bg-indigo-600 hover:bg-indigo-500 text-white
               flex items-center justify-center shadow-lg shadow-indigo-600/30
               transition-colors"
-            aria-label={lang === 'de' ? 'Investor Agent oeffnen' : 'Open Investor Agent'}
+            aria-label={lang === 'de' ? 'Investor Agent öffnen' : 'Open Investor Agent'}
           >
             <svg width="24" height="24" viewBox="0 0 24 24" fill="none" stroke="currentColor" strokeWidth="2" strokeLinecap="round" strokeLinejoin="round">
               <path d="M21 15a2 2 0 01-2 2H7l-4 4V5a2 2 0 012-2h14a2 2 0 012 2z" />