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