feat: update the .env_example

.env.example

@@ -1,7 +1,3 @@
-# LLM Provider — choose "openai" or "gemini"
-LLM_PROVIDER=openai
-OPENAI_API_KEY=your-openai-api-key-here
-
 # Gemini (only needed if LLM_PROVIDER=gemini)
 GEMINI_API_KEY=your-gemini-api-key-here
 
@@ -13,4 +9,4 @@ DATABASE_URL=postgresql://postgres:password@localhost:5432/investigator_db
 
 # Application
 APP_ENV=development
-LOG_LEVEL=info
+LOG_LEVEL=info