fix: pass base_url and api_key directly to camel-ai ModelFactory

camel-ai does not read OPENAI_BASE_URL env var reliably.
Pass api_key and base_url via model_config_dict instead.

backend/scripts/run_twitter_simulation.py

@@ -454,9 +454,16 @@ 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
+        
         return ModelFactory.create(
             model_platform=ModelPlatformType.OPENAI,
-            model_type=llm_model,
+            model_config_dict=model_config,
         )
     
     def _get_active_agents_for_round(