feat(ui): add transient loading indicator

src/components/ui/AppLoadingIndicator.tsx

@@ -0,0 +1,44 @@
+interface AppLoadingIndicatorProps {
+  className?: string | undefined;
+  floating?: boolean;
+}
+
+export function AppLoadingIndicator({
+  className,
+  floating = false,
+}: AppLoadingIndicatorProps): React.JSX.Element {
+  const classes = [
+    "app-loading-indicator",
+    floating ? "app-loading-indicator--floating" : null,
+    className,
+  ]
+    .filter(Boolean)
+    .join(" ");
+
+  return (
+    <div className={classes} role="status" aria-live="polite">
+      <span>Loading...</span>
+      <svg
+        className="app-loading-indicator__spinner"
+        viewBox="0 0 32 32"
+        aria-hidden="true"
+      >
+        <path
+          d="M16 3a13 13 0 1 1-9.2 3.8"
+          fill="none"
+          stroke="currentColor"
+          strokeLinecap="round"
+          strokeWidth="3.5"
+        />
+        <path
+          d="M6.8 6.8V2.8H2.8"
+          fill="none"
+          stroke="currentColor"
+          strokeLinecap="round"
+          strokeLinejoin="round"
+          strokeWidth="3.5"
+        />
+      </svg>
+    </div>
+  );
+}

src/components/ui/SceneLoadingOverlay.tsx

@@ -1,3 +1,4 @@
+import { AppLoadingIndicator } from "@/components/ui/AppLoadingIndicator";
 import type { SceneLoadingState } from "@/types/world/sceneLoading";
 
 const LOADING_BACKGROUND_PATH = "/assets/bg-site.png";
@@ -36,30 +37,7 @@ export function SceneLoadingOverlay({
       />
       <div className="scene-loading-overlay__footer">
         <div className="scene-loading-overlay__meta">
-          <div className="scene-loading-overlay__label">
-            <span>Loading...</span>
-            <svg
-              className="scene-loading-overlay__spinner"
-              viewBox="0 0 32 32"
-              aria-hidden="true"
-            >
-              <path
-                d="M16 3a13 13 0 1 1-9.2 3.8"
-                fill="none"
-                stroke="currentColor"
-                strokeLinecap="round"
-                strokeWidth="3.5"
-              />
-              <path
-                d="M6.8 6.8V2.8H2.8"
-                fill="none"
-                stroke="currentColor"
-                strokeLinecap="round"
-                strokeLinejoin="round"
-                strokeWidth="3.5"
-              />
-            </svg>
-          </div>
+          <AppLoadingIndicator className="scene-loading-overlay__label" />
           <strong>{progress}%</strong>
         </div>
         <div className="scene-loading-overlay__track">