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.
Two LLM tasks (greeter and support) handing off to each other over
the local `AsyncQueueBus`. The main task owns the transport
pipeline (STT, TTS, transport I/O) and the child tasks each run
their own LLM behind a `BusBridgeProcessor`. Each child uses
`bridged=()` so `PipelineTask` auto-wraps its pipeline with
the bus edge processors, and `transfer_to_agent` / `end_conversation`
tools demonstrate `handoff_to(...)` and `end(...)`.
