T7: proves slice-4's Reflex<TapAudioPipe> + LocalVadReflex decorates the
trunk leg's TapAudioPipe identically; barge-in fires on PSTN caller speech
through the same state machine as WebRTC caller speech.
T8: MockRealtimeBrain + BrainShim drives a synthetic PSTN caller through the
FOB reflex loop end-to-end: loud PCM -> local VAD trips -> barge kills ->
brain reply -> un-mute -> idle timeout (caller hangup) closes the session.
Dev-dependencies added to rutster-trunk/Cargo.toml so the integration tests
reach MockRealtimeBrain, futures-util, and tokio-tungstenite without pulling
FOB source into the trunk crate.
Signed-off-by: Aaron D. Lee <himself@adlee.work>
