Required by the stricter server-side call_sid requirements from the
previous commit. Without this, agents would fail to join or leave calls
because the client side still sent only conversation_id.
- TwilioVoiceClient.joinClientCall now forwards callSid as a Device.connect
param, which becomes params[:call_sid] on the TwiML webhook.
- VoiceAPI.leaveConference takes callSid and passes it as a query param
so the DELETE /conference endpoint can resolve the exact call.
- useCallSession and FloatingCallWidget pass callSid through.