Fix duplicate new-ticket notification (toast + desktop push both fired)

appendMessage() publishes ticket.created and message.created for the
same first message of a new ticket. TicketToasts and DesktopNotifications
listened to both independently, so one new customer ticket produced two
toasts/two chimes/two OS notifications. message.created now carries
ticketIsNew so both subscribers can skip it when ticket.created already
covered the same event.

src/lib/tickets/service.ts

@@ -164,6 +164,7 @@ async function appendMessage(params: {
     customerId: ticket.customerId,
     assigneeId: dto.assigneeId,
     message: messageDto,
+    ticketIsNew: params.ticketIsNew,
   });
 
   // Fire-and-forget: push delivery is a best-effort side channel for