fix: revert to env var approach for camel-ai LLM config

model_config_dict passes values to create() call, not client constructor.
api_key in model_config_dict causes 'unexpected keyword argument' error.
Revert to env vars: OPENAI_API_KEY + OPENAI_BASE_URL (camel-ai reads both).

backend/scripts/run_twitter_simulation.py

@@ -454,17 +454,11 @@ class TwitterSimulationRunner:
         
         print(f"LLM配置: model={llm_model}, base_url={llm_base_url[:40] if llm_base_url else '默认'}...")
         
-        # Build model config dict for camel-ai
-        model_config = {"model_type": llm_model}
-        if llm_api_key:
-            model_config["api_key"] = llm_api_key
-        if llm_base_url:
-            model_config["base_url"] = llm_base_url
+        # camel-ai reads OPENAI_API_KEY from env automatically
         
         return ModelFactory.create(
             model_platform=ModelPlatformType.OPENAI,
             model_type=llm_model,
-            model_config_dict=model_config,
         )
     
     def _get_active_agents_for_round(