first version

feat: gallery as its own section with a Photo gallery button on events

The gallery moves off the event page into a Gallery section like Results:
/gallery lists events as cards (latest photos first, collage covers,
counts, search, All / With photos / To review) and /gallery/:eventId
shows the event's photos and videos, uploads and the review queue. The
event page keeps a single Photo gallery button with the photo count.
Notification and dashboard links now open the gallery page.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>