fix: keep the speed results hidden until there is a measurement

internal/server/web/static/app.css

@@ -10,6 +10,8 @@
   --ok: #37c871;
 }
 * { box-sizing: border-box; }
+/* The hidden attribute wins over any display set by a class. */
+[hidden] { display: none !important; }
 body {
   margin: 0;
   background: var(--bg);