LehrerApp/LehrerApp.Desktop/Views/Groups/GroupListView.axaml

<UserControl xmlns="https://github.com/avaloniaui"
             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
             xmlns:vm="clr-namespace:LehrerApp.Desktop.ViewModels.Groups"
             x:Class="LehrerApp.Desktop.Views.Groups.GroupListView"
             x:DataType="vm:GroupListViewModel">

  <Grid RowDefinitions="Auto,*">

    <!-- Kopfzeile mit Schuljahr-Wähler und Neu-Button -->
    <Border Grid.Row="0" Padding="20,16"
            BorderBrush="{DynamicResource SystemControlForegroundBaseLowBrush}"
            BorderThickness="0,0,0,1">
      <Grid ColumnDefinitions="*,Auto,Auto">
        <StackPanel Grid.Column="0">
          <TextBlock Text="Lerngruppen" FontSize="22" FontWeight="SemiBold"/>
          <TextBlock FontSize="12" Opacity="0.5">
            <Run Text="{Binding Groups.Count}"/>
            <Run Text=" Gruppen · "/>
            <Run Text="{Binding SelectedSchoolYear}"/>
          </TextBlock>
        </StackPanel>
        <ComboBox Grid.Column="1" ItemsSource="{Binding SchoolYears}"
                  SelectedItem="{Binding SelectedSchoolYear}"
                  Width="100" Margin="0,0,8,0" VerticalAlignment="Center"/>
        <Button Grid.Column="2" Content="＋ Neue Gruppe"
                Command="{Binding AddGroupCommand}" VerticalAlignment="Center"/>
      </Grid>
    </Border>

    <!-- Master-Detail: Liste links, Übersicht rechts -->
    <Grid Grid.Row="1" ColumnDefinitions="260,*">

      <!-- Linke Spalte: Sucheingabe + Listenansicht -->
      <Border Grid.Column="0"
              BorderBrush="{DynamicResource SystemControlForegroundBaseLowBrush}"
              BorderThickness="0,0,1,0">
        <DockPanel>
          <TextBox DockPanel.Dock="Top" Text="{Binding SearchText}"
                   PlaceholderText="Suchen…" Margin="12,8"/>
          <ListBox ItemsSource="{Binding Groups}"
                   SelectedItem="{Binding SelectedGroup}">
            <ListBox.ItemTemplate>
              <DataTemplate DataType="vm:GroupListItem">
                <Grid ColumnDefinitions="4,*" Margin="2,4">
                  <Border Grid.Column="0" Width="4" CornerRadius="2"
                          Background="{DynamicResource SystemAccentColor}"
                          Margin="0,0,10,0"/>
                  <StackPanel Grid.Column="1">
                    <Grid ColumnDefinitions="*,Auto">
                      <TextBlock Grid.Column="0" Text="{Binding Name}"
                                 FontWeight="SemiBold" FontSize="13"/>
                      <TextBlock Grid.Column="1" Text="{Binding TypeLabel}"
                                 FontSize="11" Opacity="0.5"/>
                    </Grid>
                    <TextBlock Text="{Binding Subject}" FontSize="12" Opacity="0.65"
                               IsVisible="{Binding Subject, Converter={x:Static StringConverters.IsNotNullOrEmpty}}"/>
                    <TextBlock Text="{Binding GradingLabel}" FontSize="11" Opacity="0.4"/>
                  </StackPanel>
                </Grid>
              </DataTemplate>
            </ListBox.ItemTemplate>
          </ListBox>
        </DockPanel>
      </Border>

      <!-- Rechte Spalte: Platzhalter wenn keine Auswahl -->
      <StackPanel Grid.Column="1" HorizontalAlignment="Center"
                  VerticalAlignment="Center" Spacing="8"
                  IsVisible="{Binding SelectedGroup, Converter={x:Static ObjectConverters.IsNull}}">
        <TextBlock Text="Gruppe auswählen" FontSize="16" Opacity="0.4"
                   HorizontalAlignment="Center"/>
        <TextBlock Text="oder ＋ Neue Gruppe anlegen" FontSize="12" Opacity="0.3"
                   HorizontalAlignment="Center"/>
      </StackPanel>

      <!-- Rechte Spalte: Gruppen-Übersicht wenn ausgewählt -->
      <ScrollViewer Grid.Column="1"
                    IsVisible="{Binding SelectedGroup, Converter={x:Static ObjectConverters.IsNotNull}}">
        <StackPanel Margin="28,24" Spacing="20">

          <!-- Gruppenname und Kurzinfos -->
          <StackPanel Spacing="4">
            <TextBlock Text="{Binding SelectedGroupDisplayName}"
                       FontSize="24" FontWeight="SemiBold" TextWrapping="Wrap"/>
            <TextBlock Text="{Binding SelectedGroupSubtitle}"
                       FontSize="12" Opacity="0.55"/>
          </StackPanel>

          <Separator/>

          <!-- Bereichs-Navigation -->
          <TextBlock Text="BEREICHE" FontSize="10" FontWeight="Bold"
                     Opacity="0.4" Margin="0,0,0,2"/>
          <StackPanel Spacing="6">
            <Button Content="👤  Schülerliste"
                    HorizontalAlignment="Stretch" HorizontalContentAlignment="Left"
                    Padding="12,9"
                    Command="{Binding NavigateToSectionCommand}"
                    CommandParameter="1"/>
            <Button Content="📝  Klausuren"
                    HorizontalAlignment="Stretch" HorizontalContentAlignment="Left"
                    Padding="12,9"
                    Command="{Binding NavigateToSectionCommand}"
                    CommandParameter="2"/>
            <Button Content="🔢  Notenübersicht"
                    HorizontalAlignment="Stretch" HorizontalContentAlignment="Left"
                    Padding="12,9"
                    Command="{Binding NavigateToSectionCommand}"
                    CommandParameter="3"/>
            <Button Content="📅  Unterrichtsplanung"
                    HorizontalAlignment="Stretch" HorizontalContentAlignment="Left"
                    Padding="12,9"
                    Command="{Binding NavigateToSectionCommand}"
                    CommandParameter="4"/>
            <Button Content="📋  Dokumentation"
                    HorizontalAlignment="Stretch" HorizontalContentAlignment="Left"
                    Padding="12,9"
                    Command="{Binding NavigateToSectionCommand}"
                    CommandParameter="5"/>
          </StackPanel>

        </StackPanel>
      </ScrollViewer>

    </Grid>
  </Grid>
</UserControl>