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/main.tsx

@@ -121,7 +121,7 @@ createRoot(document.getElementById("root")!).render(
     {/* Around EVERY entry, the public ones too: a crash on a shared /watch link, or its chunk gone
         twice over after a release (lib/staleBuild), left a blank white page with no way on. */}
     <ErrorBoundary>
-      <Suspense fallback={<div style={{ minHeight: "100vh" }} />}>{root}</Suspense>
+      <Suspense fallback={<div style={{ minHeight: "100dvh" }} />}>{root}</Suspense>
     </ErrorBoundary>
   </React.StrictMode>,
 );