added more logging for debugging voice issues

backend/app/services/voice_service.py

@@ -1,6 +1,7 @@
 """FluentGerman.ai — Voice service (API provider + browser fallback)."""
 
 import io
+import logging
 
 import openai
 
@@ -12,6 +13,11 @@ async def transcribe(audio_bytes: bytes, filename: str = "audio.webm") -> str:
     settings = get_settings()
     # Use dedicated OpenAI key if available, otherwise fallback to LLM key
     api_key = settings.openai_api_key or settings.llm_api_key
+
+    key_type = "OPENAI_API_KEY" if settings.openai_api_key else "LLM_API_KEY"
+    masked = f"{api_key[:4]}...{api_key[-4:]}" if api_key and len(api_key) > 8 else "EMPTY"
+    logging.getLogger("fluentgerman.voice").info(f"Transcribing with {key_type}: {masked}")
+
     client = openai.AsyncOpenAI(api_key=api_key)
 
     audio_file = io.BytesIO(audio_bytes)
@@ -29,6 +35,11 @@ async def synthesize(text: str) -> bytes:
     settings = get_settings()
     # Use dedicated OpenAI key if available, otherwise fallback to LLM key
     api_key = settings.openai_api_key or settings.llm_api_key
+
+    key_type = "OPENAI_API_KEY" if settings.openai_api_key else "LLM_API_KEY"
+    masked = f"{api_key[:4]}...{api_key[-4:]}" if api_key and len(api_key) > 8 else "EMPTY"
+    logging.getLogger("fluentgerman.voice").info(f"Synthesizing with {key_type}: {masked}")
+
     client = openai.AsyncOpenAI(api_key=api_key)
 
     response = await client.audio.speech.create(