- Add isPrePopulated parameter to CalendarTaskRow (default false, backward compat)
- Wrap ListTile in Opacity(0.55) when isPrePopulated to indicate upcoming tasks
- Render 'Demnächst' section in CalendarDayList with muted section header
- Update _buildAnimatedTaskRow to accept and forward isPrePopulated flag
- Update _CompletingTaskRow to accept isPrePopulated (always false during animation)
- Update celebration check to include prePopulatedTasks.isEmpty condition
- Update _completingTaskIds cleanup to also check prePopulatedTasks