fix(config): add groq whisper example for voice transcription

Shows correct model entry format (openai/ prefix + api_base override)
needed to route Groq Whisper requests properly.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

config/config.example.json

@@ -85,6 +85,12 @@
       "model": "openai/gpt-5.4",
       "api_key": "sk-key2",
       "api_base": "https://api2.example.com/v1"
+    },
+    {
+      "model_name": "groq-whisper",
+      "model": "openai/whisper-large-v3-turbo",
+      "api_key": "your-groq-api-key",
+      "api_base": "https://api.groq.com/openai/v1"
     }
   ],
   "channels": {
@@ -490,7 +496,7 @@
     "monitor_usb": true
   },
   "voice": {
-    "model_name": "",
+    "model_name": "groq-whisper",
     "echo_transcription": false
   },
   "hooks": {