web: the landing page hands out no more pixels than it draws

A save cannot be beaten — the bytes are already on the machine — so the page
stops handing over the uploader's 4000px original: each photo is decoded,
redrawn at the size of the box it sits in times the screen's pixel ratio (2x at
most) and only that smaller copy reaches the tag. A visitor who saves one gets
a screen-sized file.

Right-click, drag and long-press are turned off on top of it, and the QR code
card — a link image, not a contribution — is left as it was.

docker/frontend/src/styles/landing.css

@@ -293,6 +293,9 @@ html { scroll-behavior: smooth; scroll-padding-top: 116px; }
 }
 .lp-shot { position: relative; aspect-ratio: 4 / 5; border-radius: 5px; overflow: hidden; background: #000; }
 .lp-shot img { width: 100%; height: 100%; object-fit: cover; display: block; }
+/* Contributed photos, whatever the section: the page draws them but does not
+   invite a save — no drag image, no long-press callout, no text selection. */
+.lp-photo { -webkit-user-drag: none; user-select: none; -webkit-touch-callout: none; }
 .lp-grain {
   position: absolute;
   inset: 0;