further improved accessibility across the application and add tooltips to action buttons

lib/view/pages/timetable/timetable.dart

@@ -106,6 +106,10 @@ class _TimetableState extends State<Timetable> {
         .canViewForeignTimetables;
     return Scaffold(
       appBar: AppBar(
+        // Der Kalender scrollt nicht (nur ziehen/reloaden), aber seine internen
+        // Scrollables feuern ScrollNotifications, die sonst den Material-3
+        // "scrolled under"-Farbwechsel der AppBar dauerhaft auslösen.
+        notificationPredicate: (_) => false,
         title: const Text('Stunden & Vertretungsplan'),
         actions: [
           IconButton(
@@ -114,6 +118,7 @@ class _TimetableState extends State<Timetable> {
             onPressed: atToday ? null : _jumpToToday,
           ),
           PopupMenuButton<_CalendarAction>(
+            tooltip: 'Kalendereinträge',
             icon: const Icon(Icons.edit_calendar_outlined),
             onSelected: _onAction,
             itemBuilder: (_) => const [
@@ -176,6 +181,9 @@ class _TimetableState extends State<Timetable> {
         .canViewForeignTimetables;
     return Scaffold(
       appBar: AppBar(
+        // Siehe _buildOwnPlan: den scroll-under-Farbwechsel unterdrücken, weil
+        // der Kalender nicht scrollt, aber ScrollNotifications feuert.
+        notificationPredicate: (_) => false,
         title: const Text('Stunden & Vertretungsplan'),
         actions: [
           IconButton(
@@ -285,7 +293,9 @@ class _ViewingBanner extends StatelessWidget {
             ),
             compactButton(
               icon: isFavorite ? Icons.star : Icons.star_border,
-              tooltip: isFavorite ? 'Favorit entfernen' : 'Als Favorit markieren',
+              tooltip: isFavorite
+                  ? 'Favorit entfernen'
+                  : 'Als Favorit markieren',
               onPressed: () => _toggleFavorite(context),
             ),
             const SizedBox(width: 4),