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/pages/PlaceholderPage.tsx

@@ -0,0 +1,12 @@
+import { useTranslation } from 'react-i18next';
+import { Card } from '@/components/ui/Card';
+
+export function PlaceholderPage({ titleKey }: { titleKey: string }) {
+  const { t } = useTranslation();
+
+  return (
+    <Card title={t(titleKey)}>
+      <p style={{ color: 'var(--text-secondary)' }}>{t('common.loading')}</p>
+    </Card>
+  );
+}