Add LangChain adapter examples

[wu-xiaochen]

🎯 Goal

Add practical examples showing how to use Clawra alongside LangChain.

📝 Details

The LangChain adapter exists in src/sdk/adapters/langchain.py but needs:

1. A complete working example (examples/demo_langchain_adapter.py)
2. Documentation showing how to use Clawra's reasoning within a LangChain agent
3. Use case: when to use Clawra + LangChain together vs. either alone

🔗 References

• Existing adapter: src/sdk/adapters/langchain.py

Labels

enhancement, good first issue