replaced account data singleton with a session model

lib/main.dart

@@ -26,7 +26,6 @@ import 'api/marianumconnect/queries/telemetry_heartbeat/telemetry_heartbeat.dart
 import 'app.dart';
 import 'background/widget_background_task.dart';
 import 'firebase_options.dart';
-import 'model/account_data.dart';
 import 'model/session_wipe.dart';
 import 'notification/notification_service.dart';
 import 'push/push_message_handler.dart';
@@ -34,6 +33,7 @@ import 'push/push_registration.dart';
 import 'push/push_registration_store.dart';
 import 'push/push_renderer.dart';
 import 'routing/app_routes.dart';
+import 'session/session_manager.dart';
 import 'share_intent/share_intent_listener.dart';
 import 'state/app/modules/account/bloc/account_bloc.dart';
 import 'state/app/modules/account/bloc/account_state.dart';
@@ -119,7 +119,7 @@ void _installErrorHandlers() {
 Future<void> main() async {
   log('MarianumMobile started');
   WidgetsFlutterBinding.ensureInitialized();
-  AccountData().markUiEngine();
+  SessionManager().markUiEngine();
   // Before any initialisation so startup failures reach the backend too.
   _installErrorHandlers();
 
@@ -152,12 +152,12 @@ Future<void> main() async {
     _startupStep('documents dir', () async {
       AppPaths.documentsDir = (await getApplicationDocumentsDirectory()).path;
     }),
-    // The keychain may still be locked right after device unlock; AccountData
+    // The keychain may still be locked right after device unlock; the session
     // keeps retrying, so on timeout the app starts on the loading screen and
     // flips to the real state once the session is readable (see _MainState).
     _startupStep(
       'account data',
-      AccountData().waitForPopulation,
+      SessionManager().waitForLoad,
       timeout: const Duration(seconds: 5),
       // Expected on every background wake of a locked device; not an error.
       report: false,
@@ -224,7 +224,7 @@ Future<void> main() async {
   // 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()) {
+  if (SessionManager().hasNextcloud) {
     unawaited(
       ListFilesCache.prefetchRootListing().onError(
         (e, _) => log('Files root prefetch failed: $e'),
@@ -262,9 +262,9 @@ Future<void> main() async {
 }
 
 AccountStatus _initialAccountStatus() {
-  final account = AccountData();
-  if (account.isPopulated()) return AccountStatus.loggedIn;
-  return account.isLoaded ? AccountStatus.loggedOut : AccountStatus.undefined;
+  final session = SessionManager();
+  if (session.isSignedIn) return AccountStatus.loggedIn;
+  return session.isLoaded ? AccountStatus.loggedOut : AccountStatus.undefined;
 }
 
 class Main extends StatefulWidget {
@@ -293,13 +293,13 @@ class _MainState extends State<Main> {
     Jiffy.setLocale('de');
     _lastStatus = context.read<AccountBloc>().state.status;
 
-    AccountData().waitForPopulation().then((value) {
+    SessionManager().waitForLoad().then((session) {
       if (!mounted) return;
       final accountBloc = context.read<AccountBloc>();
       accountBloc.setStatus(
-        value ? AccountStatus.loggedIn : AccountStatus.loggedOut,
+        session != null ? AccountStatus.loggedIn : AccountStatus.loggedOut,
       );
-      if (value) {
+      if (session != null) {
         _scheduleSessionValidation(accountBloc);
         // Cold start while already logged in: the account status doesn't
         // change, so the loggedIn listener below never fires — refresh
@@ -323,7 +323,9 @@ class _MainState extends State<Main> {
   void _prefetchBaseData(BuildContext context) {
     context.read<TimetableBloc>().refresh();
     unawaited(context.read<ChatListBloc>().refresh(silent: true));
-    unawaited(ListFilesCache.prefetchRootListing());
+    if (SessionManager().hasNextcloud) {
+      unawaited(ListFilesCache.prefetchRootListing());
+    }
   }
 
   /// Registers/self-heals the push subscription whenever the backend advertises