Fix: Remove unused import

The `startNetworkMonitoring` import was removed from `src/App.tsx` because it does not exist in the `syncUtils` module.

src/App.tsx

@@ -20,7 +20,7 @@ import PaymentMethods from './pages/PaymentMethods';
 import Settings from './pages/Settings';
 import { BudgetProvider } from './contexts/BudgetContext';
 import PrivateRoute from './components/auth/PrivateRoute';
-import { initSyncState, startNetworkMonitoring } from './utils/syncUtils';
+import { initSyncState } from './utils/syncUtils';
 
 // 전역 오류 핸들러
 const handleError = (error: Error | unknown) => {
@@ -157,4 +157,4 @@ function App() {
       </AuthContextWrapper>
     </ErrorBoundary>;
 }
-export default App;
+export default App;