implemented background prefetching for files root, added 24-hour caching for root directory listing, and enabled cache renewal for manual refreshes

lib/main.dart

@@ -17,6 +17,7 @@ import 'package:path_provider/path_provider.dart';
 import 'package:persistent_bottom_nav_bar_v2/persistent_bottom_nav_bar_v2.dart';
 import 'package:shared_preferences/shared_preferences.dart';
 
+import 'api/marianumcloud/webdav/queries/list_files/list_files_cache.dart';
 import 'api/mhsl/breaker/get_breakers/get_breakers_response.dart';
 import 'app.dart';
 import 'background/widget_background_task.dart';
@@ -91,6 +92,20 @@ Future<void> main() async {
     ),
   );
 
+  // Warm up the Nextcloud root listing in the background while the user is
+  // still on the launch screen / other modules — the root endpoint is slow
+  // on our instance, so kicking it off early means the Files page already
+  // has data ready by the time the user navigates to it. No-op when a
+  // cached payload is already present, so this does not undo the day-long
+  // root cache TTL.
+  if (AccountData().isPopulated()) {
+    unawaited(
+      ListFilesCache.prefetchRootListing().onError(
+        (e, _) => log('Files root prefetch failed: $e'),
+      ),
+    );
+  }
+
   if (kReleaseMode) {
     ErrorWidget.builder = (error) => Material(
       color: Colors.white,