feat(tts): add read-latest voice command

docs/channels/whatsapp.md

@@ -365,6 +365,7 @@ When the linked self number is also present in `allowFrom`, WhatsApp self-chat s
     - reply payloads preserve `audioAsVoice`; TTS voice-note output for WhatsApp stays on this PTT path even when the provider returns MP3 or WebM
     - native Ogg/Opus audio is sent as `audio/ogg; codecs=opus` for voice-note compatibility
     - non-Ogg audio, including Microsoft Edge TTS MP3/WebM output, is transcoded with `ffmpeg` to 48 kHz mono Ogg/Opus before PTT delivery
+    - `/tts latest` sends the latest assistant reply as one voice note and suppresses repeat sends for the same reply; `/tts chat on|off|default` controls auto-TTS for the current WhatsApp chat
     - animated GIF playback is supported via `gifPlayback: true` on video sends
     - captions are applied to the first media item when sending multi-media reply payloads, except PTT voice notes send the audio first and visible text separately because WhatsApp clients do not render voice-note captions consistently
     - media source can be HTTP(S), `file://`, or local paths