Document urgent flag in operations guide

Added example for urgent messages with higher volume playback.
Also updated voice example to use lessac-high.

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Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

OPERATIONS.md

@@ -94,10 +94,23 @@ curl -X POST http://localhost:8888/notify \
   -d '{
     "message": "Speaking at a different rate",
     "rate": 200,
-    "voice": "en_US-lessac-medium"
+    "voice": "en_US-lessac-high"
   }'
 ```
 
+### Example: Urgent Message (Higher Volume)
+
+```bash
+curl -X POST http://localhost:8888/notify \
+  -H 'Content-Type: application/json' \
+  -d '{
+    "message": "Critical alert! Immediate attention required.",
+    "urgent": true
+  }'
+```
+
+The `urgent` flag plays audio at 1.5x volume for critical messages.
+
 ## Configuration
 
 Configuration is via environment variables. Edit the service file or create a `.env` file: