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

lib/view/pages/timetable/timetable.dart

@@ -152,8 +152,12 @@ class _TimetableState extends State<Timetable> {
           key: _calendarKey,
           state: state,
           onWeekChanged: bloc.changeWeek,
-          onAppointmentTap: (apt) =>
-              AppointmentDetailsDispatcher.show(context, state, apt),
+          onAppointmentTap: (apt) => AppointmentDetailsDispatcher.show(
+            context,
+            state,
+            apt,
+            canEditSubjectColor: true,
+          ),
           onCreateEvent: _onCreateEventAt,
           customEvents: state.customEvents?.events ?? const [],
         ),