The old public/app-preview-mobile.png was exactly 327x714px -- 1:1 with
its CSS display size, so retina displays (2x/3x DPR) had no headroom and
Lighthouse flagged it as "serves images with low resolution"
(image-size-responsive, SpeedUp-Plan P2).
Replaced with a fresh feed screenshot supplied by the user, center-cropped
to the same 327:714 aspect ratio and delivered at 981x2142 (3x) as WebP
(~193 KB) so next/image's built-in optimizer has real headroom to generate
a proper srcset instead of upscaling a 1x source.