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/admin/scanner/page.tsx

@@ -671,10 +671,11 @@ export default function AdminScannerPage() {
 
   // Load events
   useEffect(() => {
-    eventsApi.getAll({ status: 'published' })
+    eventsApi.getAll()
       .then((res) => {
-        setEvents(res.events);
-        const upcoming = res.events.filter((e) => new Date(e.startDatetime) >= new Date());
+        const bookable = res.events.filter((e) => e.status === 'published' || e.status === 'unlisted');
+        setEvents(bookable);
+        const upcoming = bookable.filter((e) => new Date(e.startDatetime) >= new Date());
         if (upcoming.length === 1) {
           setSelectedEventId(upcoming[0].id);
         }