fix: handle null dates in dashboard and gallery pages

Add null checks for expires_at and event_date fields to prevent
TypeError when calling parseISO() on null values. This fixes crashes
that occurred after making event dates optional.

- AdminDashboard: skip events with null expires_at in expiring filter
- GalleryPage: handle null expires_at in expiration calculation
- GalleryView: make daysUntilExpiration nullable with explicit checks
- EventDetailsPage: return null from safeParseDate for null inputs

frontend/src/components/gallery/GalleryView.tsx

@@ -310,10 +310,12 @@ export const GalleryView: React.FC<GalleryViewProps> = ({ slug, event }) => {
     }
   }, [settingsData, data, setTheme]); // Use data instead of event prop
 
-  // Calculate days until expiration
-  const daysUntilExpiration = differenceInDays(parseISO(event.expires_at), new Date());
-  const showUrgentWarning = daysUntilExpiration <= 7;
-  const isExpired = daysUntilExpiration < 0;
+  // Calculate days until expiration (null means never expires)
+  const daysUntilExpiration = event.expires_at
+    ? differenceInDays(parseISO(event.expires_at), new Date())
+    : null;
+  const showUrgentWarning = daysUntilExpiration !== null && daysUntilExpiration <= 7;
+  const isExpired = daysUntilExpiration !== null && daysUntilExpiration < 0;
 
   // Filter and sort photos
   const filteredPhotos = useMemo(() => {
@@ -602,7 +604,7 @@ export const GalleryView: React.FC<GalleryViewProps> = ({ slug, event }) => {
         headerExtra={(() => {
           const items = [];
           
-          if (daysUntilExpiration <= 1 && daysUntilExpiration > 0) {
+          if (daysUntilExpiration !== null && daysUntilExpiration <= 1 && daysUntilExpiration > 0) {
             items.push(
               <CountdownTimer key="countdown" expiresAt={event.expires_at} className="mr-2" />
             );