Switch every example to ``await runner.spawn(task)`` followed by
``await runner.run()`` (no task argument), and ``await runner.cancel()``
on client-disconnected instead of ``await task.cancel()``. This makes
the main pipeline task look the same as the worker / proxy tasks
spawned alongside it, and lets ``runner.cancel()`` drive a uniform
shutdown across every root task on the bus.
Demonstrates the WebSocket proxy tasks: a local `main.py` voice
bot uses `WebSocketProxyClientTask` to forward bus messages
(including `BusFrameMessage`s) to a remote `assistant.py`
FastAPI server. Each incoming connection spawns a
`WebSocketProxyServerTask` plus an `LLMTask` assistant on a
per-session `PipelineRunner`.
