Masonry — reflow during image loads

Two grids, same photos, separate Run buttons so you feel each one. The left uses stock <img> tags with no reserved dimensions — the column stretches as each image decodes and every tile below it shifts. The right calls prepare() per image first, then commits the layout from @somnai-dreams/layout-algebra in one synchronous pass; tiles are positioned before any pixel paints. Toggle between shortest-column masonry (packShortestColumn) and Flickr-style justified rows (packJustifiedRows).