Tests cover all Send() code paths:
- Nil TTS synthesizer returns tts-not-wired error
- Nil sessions registry returns sessions-not-wired error
- No live session returns delivery.ErrVoiceNoSession (dispatcher reroutes)
- With session: pushes audio_nudge frame with correct kind, rule_name,
text, PCM16kMono format, non-empty audio bytes
- Empty Body falls back to Summary text
- TTS synthesize error propagates with 'synthesize:' prefix
- Invalid audio format rejects with 'refuse to ship' error
Uses net.Pipe() for real voice.Sessions integration, tts.Stub for
deterministic synthesis, and fake synthesizers for error paths.
kami