- Add `has_audio_input` flag to agent message handling and propagate through processing pipeline
- Structure agent input payloads to include `input.mode` and `input.transcribed` for voice messages
- Update prompts and tool descriptions to clarify that `send_voice_message` and `ask_user_choice` are terminal tools and should not be followed by redundant text replies
- Enhance tests to cover voice input metadata propagation and prompt updates