Pulse STT

The per-word confidence score is now documented across the Speech-to-Text API reference. These fields were already returned by the API — this makes them explicit in the reference.

• Sync REST (POST /waves/v1/stt): the words[] entries (returned when word_timestamps=true) carry word, start, end, and a confidence score from 0.0 to 1.0. The confidence field is now described in the Word schema, and the word_timestamps parameter documents the full per-word shape it surfaces.
• Streaming (WSS /waves/v1/stt/live): the words[] schema now lists confidence, plus speaker_confidence (returned alongside speaker when diarize=true).

Documentation only — no API behaviour changed.