feat: initialize new React application structure with TypeScript, ESLint, and Prettier configurations, while removing legacy files and adding new components and pages for enhanced functionality

src/components/ui/LoadingSpinner.tsx

@@ -0,0 +1,10 @@
+export function LoadingSpinner({ size = 20 }: { size?: number }) {
+  return (
+    <div
+      className="loading-spinner"
+      style={{ width: size, height: size, borderWidth: size / 7 }}
+      role="status"
+      aria-live="polite"
+    />
+  );
+}