[Bug]: Fix stale LangGraph Python Dojo run instructions

### Pre-flight Checklist

- [x] I have searched [existing issues](https://github.com/ag-ui-protocol/ag-ui/issues) and this hasn't been reported yet.
- [x] I am using the **latest** version AG-UI.

### Describe the Bug

The LangGraph Python package `README` contains outdated instructions for running the Dojo examples.

### Steps to Reproduce

1. Clone the repository and open its root directory.
2. Follow the “To run the dojo examples” instructions in integrations/langgraph/python/README.md:
```

cd python/ag_ui_langgraph/examples
poetry install
poetry run dev
```

3. The first command fails because `python/ag_ui_langgraph/examples` does not exist.

### Expected Behavior

The README should point to the existing examples directory and document the appropriate command for each integration:

- LangGraph Platform (/langgraph/...):

cd integrations/langgraph/python/examples
pnpx @langchain/langgraph-cli@1.1.13 dev

- FastAPI (/langgraph-fastapi/...): document the current FastAPI/uv startup path.

### Environment

```text
Repository: ag-ui (main)
Node.js: 22.x
pnpm: 10.33.4
LangGraph CLI: @langchain/langgraph-cli@1.1.13
Runtime: Python (see pyproject.toml: Python 3.12)
```

### Screenshots

_No response_

### Logs & Errors

```shell
cd: no such file or directory: python/ag_ui_langgraph/examples
```

### Additional Context

The current examples README at integrations/langgraph/python/examples/README.md already points to the correct directory for the LangGraph Platform flow. The package README should
link to that document or align its instructions with it.