fix: pass api_key/base_url via model_config_dict, not env vars

camel-ai v0.2.78 reads OPENAI_API_KEY from env and auto-passes it to
chat.completions.create() which doesn't accept it (TypeError).

Fix: pass api_key and base_url through model_config_dict so camel-ai
extracts them for the OpenAI client constructor only.

backend/scripts/run_reddit_simulation.py

@@ -449,23 +449,23 @@ class RedditSimulationRunner:
         if not llm_model:
             llm_model = self.config.get("llm_model", "gpt-4o-mini")
         
-        # 设置 camel-ai 所需的环境变量
-        if llm_api_key:
-            os.environ["OPENAI_API_KEY"] = llm_api_key
-        
-        if not os.environ.get("OPENAI_API_KEY"):
-            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_BASE_URL"] = llm_base_url
+        if not llm_api_key:
+            raise ValueError("LLM_API_KEY not configured. Set it in .env file.")
         
         print(f"LLM配置: model={llm_model}, base_url={llm_base_url[:40] if llm_base_url else '默认'}...")
         
-        # camel-ai reads OPENAI_API_KEY from env automatically
+        # Pass api_key and base_url via model_config_dict
+        # camel-ai extracts these for the OpenAI client constructor
+        model_config = {}
+        if llm_api_key:
+            model_config["api_key"] = llm_api_key
+        if llm_base_url:
+            model_config["base_url"] = llm_base_url
         
         return ModelFactory.create(
             model_platform=ModelPlatformType.OPENAI,
             model_type=llm_model,
+            model_config_dict=model_config,
         )
     
     def _get_active_agents_for_round(