fix(design): the table header takes the B9 fade utility, and every size is dvh, not vh (E28 S3d4)

The table header carried an arbitrary-value copy of fade-below; a contract refuses a hand gradient of a surface colour. 100vh is the viewport with a tablet browser's toolbar retracted, so h-screen / min-h-screen / static vh hid the last rows under it; a contract holds dvh (the Plex player stage changes with S3f, where it is played on the tablet).

frontend/src/components/Welcome.tsx

@@ -70,7 +70,7 @@ export default function Welcome({ verify }: { verify: VerifyEntry }) {
   const [zoomed, setZoomed] = useState<{ src: string; label: string } | null>(null);
   const open = (src: string, label: string) => setZoomed({ src, label });
   return (
-    <div className="min-h-screen bg-bg text-fg overflow-y-auto">
+    <div className="min-h-dvh bg-bg text-fg overflow-y-auto">
       <header className="flex items-center justify-between px-5 sm:px-8 py-4">
         <div className="text-xl font-bold tracking-tight">
           Sift<span className="text-accent">lode</span>
@@ -324,7 +324,7 @@ function Lightbox({ src, label, onClose }: { src: string; label: string; onClose
         <img
           src={src}
           alt={label}
-          className="max-h-[82vh] max-w-[92vw] w-auto h-auto rounded-xl border border-border object-contain shadow-2xl"
+          className="max-h-[82dvh] max-w-[92vw] w-auto h-auto rounded-xl border border-border object-contain shadow-2xl"
         />
         <figcaption className="text-sm text-muted">{label}</figcaption>
       </figure>