Update LG_agent.py

LG_agent.py

@@ -8,6 +8,10 @@ from tools import all_tools
 import os
 
 # 1. Setup once
+OPENAI_API_KEY = os.getenv("OPENAI_API_KEY")
+if not OPENAI_API_KEY:
+    raise ValueError("Missing OPENAI_API_KEY environment variable.")
+
 chat = ChatOpenAI(
     model="gpt-3.5-turbo",
     openai_api_key=OPENAI_API_KEY,