fix: fix import from agui client (#164)

Author: ranst91

typescript-sdk/integrations/langgraph/src/index.ts

@@ -1,4 +1,4 @@
-import { HttpAgent } from "@ag-ui/client/src";
+import { HttpAgent } from "@ag-ui/client";
 
 export * from './agent'
 export class LangGraphHttpAgent extends HttpAgent {}