feat: add voice mode with push-to-talk and TTS output for CLI

Implements Issue #314 Phase 2 & 3:
- /voice command to toggle voice mode (on/off/tts/status)
- Ctrl+Space push-to-talk recording via sounddevice
- Whisper STT transcription via existing transcription_tools
- Optional TTS response playback via existing tts_tool
- Visual indicators in prompt (recording/transcribing/voice)
- 21 unit tests, all mocked (no real mic/API)
- Optional deps: sounddevice, numpy (pip install hermes-agent[voice])

hermes_cli/commands.py

@@ -37,6 +37,7 @@ COMMANDS_BY_CATEGORY = {
         "/verbose": "Cycle tool progress display: off → new → all → verbose",
         "/reasoning": "Manage reasoning effort and display (usage: /reasoning [level|show|hide])",
         "/skin": "Show or change the display skin/theme",
+        "/voice": "Toggle voice mode (Ctrl+B to record). Usage: /voice [on|off|tts|status]",
     },
     "Tools & Skills": {
         "/tools": "List available tools",