implemented custom subject colors for the timetable and unified the color palette system

lib/routing/app_routes.dart

@@ -36,6 +36,7 @@ import '../view/pages/talk/details/message_reactions.dart';
 import '../view/pages/talk/talk_navigator.dart';
 import '../view/pages/ticker/ticker_page_view.dart';
 import '../view/pages/timetable/custom_events/custom_events_view.dart';
+import '../view/pages/timetable/subject_colors/subject_colors_view.dart';
 import '../widget/debug/cache_view.dart';
 import '../widget/file_viewer.dart';
 import '../widget/user_avatar.dart';
@@ -90,6 +91,10 @@ class AppRoutes {
     pushScreen(context, withNavBar: false, screen: const CustomEventsView());
   }
 
+  static void openSubjectColors(BuildContext context) {
+    pushScreen(context, withNavBar: false, screen: const SubjectColorsView());
+  }
+
   /// Opens the picker for choosing a foreign timetable element and resolves to
   /// the selected element (or null if dismissed). The timetable view renders
   /// the chosen plan inline. Gated behind the `viewForeignTimetables`