Implement message preview feature for support tickets

- Added a new property `MessagePreview` to the `TicketSummaryDto` to display the truncated first message of a ticket.
- Updated the `TicketMapping` class to retrieve the first message for each ticket and truncate it for preview purposes.
- Modified the `SupportTicketList` and `AdminSupportPage` components to conditionally render the message preview in the ticket list, enhancing user experience by providing context at a glance.

frontend/src/routes/admin/support.tsx

@@ -55,7 +55,8 @@ function AdminSupportPage() {
                 </CardTitle>
                 <TicketStatusBadge status={ticket.status} />
               </CardHeader>
-              <CardContent>
+              <CardContent className="flex flex-col gap-1">
+                {ticket.messagePreview && <p className="truncate text-xs text-muted-foreground">{ticket.messagePreview}</p>}
                 <p className="text-xs text-muted-foreground">
                   {t('support.lastActivity', { date: new Date(ticket.lastActivityAt).toLocaleString() })}
                 </p>