Photo grid, Flickity lightbox

Hi Dave,

Is there a way to have a photo thumbnail grid and when clicking on the thumb, it opens a lightbox/overlay with the correct image? I remember this was possible using `fizzyUIUtils` but that was on an older version. Wanting to attempt something like: https://feimosi.github.io/baguetteBox.js/

Start by reviewing the Flickity fullscreen behavior and the linked baguetteBox.js example to determine how thumbnail selection should map to the displayed image. Done means supporting a photo thumbnail grid where clicking a thumbnail opens a fullscreen overlay showing the correct image, with the approach confirmed against the current Flickity version.

Written by the indexing model from the issue text.