improved visualization in admin menu and change model of transcribe

backend/app/config.py

@@ -35,7 +35,7 @@ class Settings(BaseSettings):
     voice_mode: Literal["api", "browser"] = "api"
     tts_model: str = "tts-1"
     tts_voice: str = "alloy"
-    stt_model: str = "whisper-1"
+    stt_model: str = "gpt-4o-mini-transcribe"
 
     # Admin bootstrap
     admin_email: str = "admin@fluentgerman.ai"

backend/app/services/voice_service.py

@@ -26,6 +26,7 @@ async def transcribe(audio_bytes: bytes, filename: str = "audio.webm") -> str:
     transcript = await client.audio.transcriptions.create(
         model=settings.stt_model,
         file=audio_file,
+        prompt="FluentGerman.ai — German language tutor. Deutsch, Grammatik, Übung, Aussprache.",
     )
     return transcript.text