feat: add per-event custom logo upload with bug fixes

Add event-level custom logo upload/delete endpoints and UI, allowing
per-event logos to override the global branding logo in gallery views.

Also fixes several bugs discovered during testing:
- fix: category_id 'individual' parsed as NaN causing photo upload failures
- fix: gallery auth race condition where photos query fired before token stored
- fix: gallery-photos query not invalidated after favorite/like mutations
- fix: e2e test race conditions with View Gallery button detachment

frontend/src/components/gallery/GalleryView.tsx

@@ -682,7 +682,7 @@ export const GalleryView: React.FC<GalleryViewProps> = ({ slug, event }) => {
             onToggleSelectionMode={() => setIsSelectionMode(!isSelectionMode)}
             showSelectionControls={!showSidebar}
             eventName={event.event_name}
-            eventLogo={brandingSettings?.logo_url}
+            eventLogo={data?.event?.hero_logo_url || brandingSettings?.logo_url}
             eventDate={event.event_date}
             expiresAt={event.expires_at}
             allowDownloads={allowDownloads}

frontend/src/components/gallery/PhotoFavorites.tsx

@@ -49,6 +49,7 @@ export const PhotoFavorites: React.FC<PhotoFavoritesProps> = ({
     },
     onSuccess: () => {
       queryClient.invalidateQueries({ queryKey: ['photo-feedback', gallerySlug, photoId] });
+      queryClient.invalidateQueries({ queryKey: ['gallery-photos'] });
     },
     onError: (error: any) => {
       // Revert optimistic update

frontend/src/components/gallery/PhotoLikes.tsx

@@ -49,6 +49,7 @@ export const PhotoLikes: React.FC<PhotoLikesProps> = ({
     },
     onSuccess: () => {
       queryClient.invalidateQueries({ queryKey: ['photo-feedback', gallerySlug, photoId] });
+      queryClient.invalidateQueries({ queryKey: ['gallery-photos'] });
     },
     onError: (error: any) => {
       // Revert optimistic update