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.
Variant of the local handoff example with per-task TTS voices.
Each child task wraps the LLM with its own `CartesiaTTSService`
in a custom pipeline override, so the main task has no TTS and
audio comes from whichever child is active over the bus.
