added voice functionality and increased avatar size

backend/app/config.py

@@ -27,6 +27,9 @@ class Settings(BaseSettings):
     llm_provider: str = "openai"  # used by litellm routing
     llm_api_key: str = ""
     llm_model: str = "gpt-4o-mini"
+    
+    # OpenAI API Key (specifically for Voice/TTS if LLM_PROVIDER is different)
+    openai_api_key: str = ""
 
     # Voice feature flag: "api" = LLM provider Whisper/TTS, "browser" = Web Speech API
     voice_mode: Literal["api", "browser"] = "api"