Update API_DOCUMENTATION.md with response_time_ms and response_time_sec fields

API_DOCUMENTATION.md

@@ -150,7 +150,9 @@ Creates a new voice onboarding session, initializes dynamic state, and returns l
   "status": "in_progress",
   "stage": "greeting",
   "greeting_text": "Hello Arun Kumar, welcome to CureSelect Cardiology department. What symptoms or discomfort are you experiencing today?",
-  "audio_url": "/v1/voice-onboarding/audio/voice_greeting_89bf1a.wav"
+  "audio_url": "/v1/voice-onboarding/audio/voice_greeting_89bf1a.wav",
+  "response_time_ms": 166.84,
+  "response_time_sec": 0.167
 }
 ```
 
@@ -175,7 +177,14 @@ Submits the patient's recorded audio or transcribed speech. The backend runs mul
   "ai_text": "I understand. Does the chest pain radiate to your left arm or jaw, and are you currently taking any blood pressure or heart medications?",
   "stage": "symptoms_inquiry",
   "completed": false,
-  "audio_url": "/v1/voice-onboarding/audio/speech_reply_30ef2.wav"
+  "audio_url": "/v1/voice-onboarding/audio/speech_reply_30ef2.wav",
+  "suggested_specialty": {
+    "type": "specialist",
+    "code": "cardiology",
+    "name": "Cardiology / Heart Care"
+  },
+  "response_time_ms": 1824.12,
+  "response_time_sec": 1.824
 }
 ```