fix: use correct env var OPENAI_BASE_URL for camel-ai LLM routing

camel-ai's OpenAI model reads OPENAI_BASE_URL, not OPENAI_API_BASE_URL.
This caused all simulation LLM calls to go to api.openai.com instead of
the configured provider (DeepSeek, Xiaomi Mimo, etc), resulting in 401.

backend/scripts/run_parallel_simulation.py

@@ -1027,7 +1027,7 @@ def create_model(config: Dict[str, Any], use_boost: bool = False):
         raise ValueError("缺少 API Key 配置，请在项目根目录 .env 文件中设置 LLM_API_KEY")
     
     if llm_base_url:
-        os.environ["OPENAI_API_BASE_URL"] = llm_base_url
+        os.environ["OPENAI_BASE_URL"] = llm_base_url
     
     print(f"{config_label} model={llm_model}, base_url={llm_base_url[:40] if llm_base_url else '默认'}...")