feat(console-web): add swinging iframe load progress

- place an indeterminate progress track below the loading label
- animate the indicator between both ends of the track
- expose an accessible progressbar label for the active view
- honor reduced-motion preferences with a static indicator

crates/wasmeld-console/web/src/styles/app.css

@@ -317,13 +317,39 @@
     @apply h-3 animate-pulse rounded-sm bg-[#dfe6e4];
   }
 
+  .loading-progress-track {
+    @apply h-1 w-40 overflow-hidden rounded-sm bg-line;
+  }
+
+  .loading-progress-indicator {
+    @apply block h-full w-[36%] rounded-sm bg-brand;
+    animation: loading-progress-swing 1s ease-in-out infinite alternate;
+  }
+
   .spin {
     animation: spin 0.8s linear infinite;
   }
 }
 
+@keyframes loading-progress-swing {
+  from {
+    transform: translateX(0);
+  }
+
+  to {
+    transform: translateX(178%);
+  }
+}
+
 @keyframes spin {
   to {
     transform: rotate(360deg);
   }
 }
+
+@media (prefers-reduced-motion: reduce) {
+  .loading-progress-indicator {
+    animation: none;
+    transform: translateX(89%);
+  }
+}