LangGraph Example

[zahlekhan]

Is your feature request related to a problem? Please describe.
There is no example showing how to use OpenUI with LangGraph. Users who want to build agentic generative UI applications with LangGraph have no reference implementation to start from, making adoption harder.

Describe the solution you'd like
Add a standalone example app in the examples/ folder (e.g., examples/langgraph-chat) that demonstrates OpenUI + LangGraph integration. The example should:

• Be a full working app (Next.js, similar to the existing examples/openui-chat).
• Use the langGraphAdapter from @openuidev/react-headless (depends on LangGraph Adapter #292).
• Demonstrate a generic multi-agent workflow — show how multiple LangGraph nodes stream generative UI through OpenUI's renderer.
• Support both LangGraph Cloud and local LangGraph setups, with clear instructions for each in the README.
• Include configuration for connecting to a LangGraph deployment (API URL, assistant ID, etc.).
• Show how OpenUI Lang output streams progressively through a LangGraph graph execution.

Describe alternatives you've considered

• Adding LangGraph usage to the existing openui-chat example, but a dedicated example keeps things focused and avoids overloading the starter app.
• A documentation-only guide without runnable code, but a working example is far more useful for developers getting started.

Additional context
This depends on the LangGraph Adapter (#292) being implemented first. The example should follow the same structure and conventions as examples/openui-chat.