Replace queue with ring buffer jitter absorption for live caller audio

- Server: 150ms pre-buffer ring buffer eliminates gaps from timing mismatches
- Browser playback: 150ms jitter buffer (up from 80ms) for network jitter
- Capture chunks: 960 samples/60ms (better network efficiency)

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

frontend/call-in.html

@@ -150,6 +150,6 @@
         </div>
     </div>
 
-    <script src="/js/call-in.js?v=2"></script>
+    <script src="/js/call-in.js?v=3"></script>
 </body>
 </html>