fix(chapter15): load backend .env so LLM_API_KEY is read at startup

code/chapter15/Helloagents-AI-Town/backend/config.py

@@ -3,6 +3,10 @@
 import os
 from typing import Optional
 
+from dotenv import load_dotenv
+
+load_dotenv(os.path.join(os.path.dirname(__file__), ".env"))
+
 class Settings:
     """应用配置"""
     
@@ -39,4 +43,3 @@ class Settings:
         return True
 
 settings = Settings()
-

code/chapter15/Helloagents-AI-Town/backend/requirements.txt

@@ -3,6 +3,7 @@ fastapi>=0.104.0
 uvicorn[standard]>=0.24.0
 pydantic>=2.0.0
 requests>=2.31.0
+python-dotenv>=1.0.0
 
 # CORS支持
 python-multipart>=0.0.6