fix: improve error handling and stability - no logout on transient errors, add ErrorBoundary, global error logging

frontend/src/App.tsx

@@ -4,6 +4,7 @@ import { AppRouter } from '@/routes';
 import { setUnauthorizedHandler } from '@/api/client';
 import { useAuthStore } from '@/store/authStore';
 import { useThemeStore } from '@/store/themeStore';
+import { ErrorBoundary } from '@/components/common/ErrorBoundary';
 
 const queryClient = new QueryClient({
   defaultOptions: {
@@ -33,7 +34,9 @@ export default function App() {
 
   return (
     <QueryClientProvider client={queryClient}>
-      <AppRouter />
+      <ErrorBoundary>
+        <AppRouter />
+      </ErrorBoundary>
     </QueryClientProvider>
   );
 }