Implement `http_driver_demo.py` example

[dgenio]

Summary

Demonstrate HTTPDriver with a local in-process HTTP server (no internet).

Behavior

1. Start a minimal HTTP server in a background thread (use stdlib http.server or similar)
2. Server responds to POST requests with a JSON payload
3. Register capability routed to HTTPDriver pointing at localhost
4. Invoke capability → print Frame
5. Shut down server cleanly on exit

Acceptance criteria

• Runs with python examples/http_driver_demo.py — exit 0
• No internet required (localhost only)
• Server starts and stops cleanly