fix: fix silence detection bugs and add Phase 4 voice mode features

Fix 3 critical bugs in silence detection:
- Micro-pause tolerance now tracks dip duration (not time since speech start)
- Peak RMS check in stop() prevents discarding recordings with real speech
- Reduced min_speech_duration from 0.5s to 0.3s for reliable speech confirmation

Phase 4 features: configurable silence params, visual audio level indicator,
voice system prompt, tool call audio cues, TTS interrupt, continuous mode
auto-restart, interruptable playback via Popen tracking.

hermes_cli/config.py

@@ -207,6 +207,8 @@ DEFAULT_CONFIG = {
         "record_key": "ctrl+r",
         "max_recording_seconds": 120,
         "auto_tts": False,
+        "silence_threshold": 200,     # RMS below this = silence (0-32767)
+        "silence_duration": 3.0,      # Seconds of silence before auto-stop
     },
     
     "human_delay": {