Add unlisted event status: hidden from listings but accessible by URL

- Backend: add 'unlisted' to schema enum and Zod validation; allow booking for unlisted events
- Frontend: Event type and guards updated; unlisted events bookable, excluded from public listing/sitemap
- Admin: badge, status dropdown, Make Unlisted / Make Public / Unpublish actions; scanner/emails/tickets include unlisted

Co-authored-by: Cursor <cursoragent@cursor.com>

frontend/src/app/(public)/book/[eventId]/page.tsx

@@ -145,7 +145,7 @@ export default function BookingPage() {
         paymentOptionsApi.getForEvent(params.eventId as string),
       ])
         .then(([eventRes, paymentRes]) => {
-          if (!eventRes.event || eventRes.event.status !== 'published') {
+          if (!eventRes.event || !['published', 'unlisted'].includes(eventRes.event.status)) {
             toast.error('Event is not available for booking');
             router.push('/events');
             return;

frontend/src/app/(public)/events/[id]/EventDetailClient.tsx

@@ -60,7 +60,7 @@ export default function EventDetailClient({ eventId, initialEvent }: EventDetail
   const isCancelled = event.status === 'cancelled';
   // Only calculate isPastEvent after mount to avoid hydration mismatch
   const isPastEvent = mounted ? new Date(event.startDatetime) < new Date() : false;
-  const canBook = !isSoldOut && !isCancelled && !isPastEvent && event.status === 'published';
+  const canBook = !isSoldOut && !isCancelled && !isPastEvent && (event.status === 'published' || event.status === 'unlisted');
 
   // Booking card content - reused for mobile and desktop positions
   const BookingCardContent = () => (

frontend/src/app/(public)/events/[id]/page.tsx

@@ -20,7 +20,7 @@ interface Event {
   price: number;
   currency: string;
   capacity: number;
-  status: 'draft' | 'published' | 'cancelled' | 'completed' | 'archived';
+  status: 'draft' | 'published' | 'unlisted' | 'cancelled' | 'completed' | 'archived';
   bannerUrl?: string;
   availableSeats?: number;
   bookedCount?: number;