use parameters as defaults and not overrides

Author: jsonbailey

packages/ai-providers/server-ai-langchain/src/LangChainProvider.ts

@@ -255,8 +255,8 @@ export class LangChainProvider extends AIProvider {
 
     // Use LangChain's universal initChatModel to support multiple providers
     return initChatModel(modelName, {
-      modelProvider: LangChainProvider.mapProvider(provider),
       ...parameters,
+      modelProvider: LangChainProvider.mapProvider(provider),
     });
   }
 }