replaced account data singleton with a session model

lib/widget_data/widget_publisher.dart

@@ -4,7 +4,7 @@ import 'dart:developer';
 import 'package:flutter/foundation.dart';
 import 'package:flutter/material.dart';
 
-import '../model/account_data.dart';
+import '../session/session_manager.dart';
 import '../state/app/modules/timetable/bloc/timetable_state.dart';
 import '../storage/settings.dart';
 import 'widget_data_mapper.dart';
@@ -48,7 +48,7 @@ class WidgetPublisher {
     bool isTeacher = false,
     int? epoch,
   }) {
-    final sessionEpoch = epoch ?? AccountData().sessionEpoch;
+    final sessionEpoch = epoch ?? SessionManager().sessionEpoch;
     return _queue = _queue.then(
       (_) => _publish(
         state,
@@ -65,7 +65,7 @@ class WidgetPublisher {
     required bool isTeacher,
     required int epoch,
   }) async {
-    if (!AccountData().isCurrentSession(epoch)) return;
+    if (!SessionManager().isCurrentSession(epoch)) return;
     try {
       final connectDouble =
           settings?.timetableSettings.connectDoubleLessons ?? true;
@@ -106,7 +106,7 @@ class WidgetPublisher {
       );
       // A publish still running at sign-out would put the previous account's
       // plan back onto the just cleared widget.
-      if (!AccountData().isCurrentSession(epoch)) return;
+      if (!SessionManager().isCurrentSession(epoch)) return;
       // Most bloc emits (week swipes, prefetches) don't touch the widget's
       // window; skip the SharedPreferences commits and widget re-render then.
       final signature = jsonEncode([