feat: add seating plans for learning groups

LehrerApp.Desktop/Views/Groups/GroupDetailView.axaml

@@ -101,6 +101,11 @@
         </DataGrid>
       </ContentPage>
 
+      <!-- Tab: Sitzpläne -->
+      <ContentPage Header="Sitzpläne">
+        <views:SeatingPlanTabView DataContext="{Binding SeatingPlanTab}"/>
+      </ContentPage>
+
       <!-- Tab: Mitarbeit -->
       <ContentPage Header="Mitarbeit">
         <views:ParticipationTabView DataContext="{Binding ParticipationTab}"/>

LehrerApp.Desktop/Views/Groups/SeatingPlanDialog.axaml

@@ -0,0 +1,55 @@
+<Window 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.SeatingPlanDialog"
+        x:DataType="vm:SeatingPlanDialogViewModel"
+        Title="{Binding DialogTitle}" Width="480" Height="470"
+        CanResize="False" WindowStartupLocation="CenterOwner">
+  <Grid RowDefinitions="*,Auto" Margin="24">
+    <StackPanel Spacing="16">
+      <StackPanel Spacing="3">
+        <TextBlock Text="{Binding DialogTitle}" Classes="dialogtitle"/>
+        <TextBlock Text="Name und Raum unterscheiden mehrere Pläne derselben Lerngruppe."
+                   FontSize="12" Opacity="0.6" TextWrapping="Wrap"/>
+      </StackPanel>
+
+      <StackPanel Spacing="4">
+        <TextBlock Text="Name *" FontSize="12" Opacity="0.7"/>
+        <TextBox Text="{Binding Name}" PlaceholderText="z. B. Standard, Gruppenarbeit"/>
+        <TextBlock Text="{Binding NameError}" Foreground="Red" FontSize="11"
+                   IsVisible="{Binding NameError, Converter={x:Static StringConverters.IsNotNullOrEmpty}}"/>
+      </StackPanel>
+
+      <StackPanel Spacing="4">
+        <TextBlock Text="Raum" FontSize="12" Opacity="0.7"/>
+        <TextBox Text="{Binding Room}" PlaceholderText="z. B. B204, Physikraum"/>
+      </StackPanel>
+
+      <Grid ColumnDefinitions="*,16,*">
+        <StackPanel Grid.Column="0" Spacing="4">
+          <TextBlock Text="Reihen" FontSize="12" Opacity="0.7"/>
+          <NumericUpDown Value="{Binding Rows}" Minimum="1" Maximum="10" Increment="1"
+                         FormatString="0"/>
+        </StackPanel>
+        <StackPanel Grid.Column="2" Spacing="4">
+          <TextBlock Text="Plätze pro Reihe" FontSize="12" Opacity="0.7"/>
+          <NumericUpDown Value="{Binding Columns}" Minimum="1" Maximum="10" Increment="1"
+                         FormatString="0"/>
+        </StackPanel>
+      </Grid>
+      <TextBlock Text="{Binding LayoutError}" Foreground="Red" FontSize="11"
+                 IsVisible="{Binding LayoutError, Converter={x:Static StringConverters.IsNotNullOrEmpty}}"/>
+
+      <Border Background="{DynamicResource SystemControlBackgroundChromeMediumLowBrush}"
+              CornerRadius="6" Padding="12">
+        <TextBlock Text="Beim Verkleinern des Rasters entfallen Zuordnungen außerhalb der neuen Größe."
+                   FontSize="12" Opacity="0.7" TextWrapping="Wrap"/>
+      </Border>
+    </StackPanel>
+
+    <Grid Grid.Row="1" ColumnDefinitions="*,8,*" Margin="0,20,0,0">
+      <Button Grid.Column="0" Content="Abbrechen" HorizontalAlignment="Stretch" Click="OnCancel"/>
+      <Button Grid.Column="2" Content="{Binding SaveButtonText}" HorizontalAlignment="Stretch" Click="OnSave"/>
+    </Grid>
+  </Grid>
+</Window>

LehrerApp.Desktop/Views/Groups/SeatingPlanDialog.axaml.cs

@@ -0,0 +1,19 @@
+using Avalonia.Controls;
+using Avalonia.Interactivity;
+using LehrerApp.Desktop.ViewModels.Groups;
+
+namespace LehrerApp.Desktop.Views.Groups;
+
+public partial class SeatingPlanDialog : Window
+{
+    public SeatingPlanDialog() => InitializeComponent();
+
+    private void OnSave(object? sender, RoutedEventArgs e)
+    {
+        if (DataContext is not SeatingPlanDialogViewModel vm) return;
+        vm.SaveCommand.Execute(null);
+        if (vm.Result is not null) Close(true);
+    }
+
+    private void OnCancel(object? sender, RoutedEventArgs e) => Close(false);
+}

LehrerApp.Desktop/Views/Groups/SeatingPlanTabView.axaml

@@ -0,0 +1,96 @@
+<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.SeatingPlanTabView"
+             x:DataType="vm:SeatingPlanTabViewModel">
+  <Grid ColumnDefinitions="260,*">
+    <Border Grid.Column="0" BorderBrush="{DynamicResource SystemControlForegroundBaseLowBrush}"
+            BorderThickness="0,0,1,0" Padding="16">
+      <Grid RowDefinitions="Auto,*,Auto">
+        <StackPanel Grid.Row="0" Spacing="4" Margin="0,0,0,12">
+          <TextBlock Text="Sitzpläne" FontSize="18" FontWeight="SemiBold"/>
+          <TextBlock Text="Mehrere Pläne, z. B. für verschiedene Räume" FontSize="12"
+                     Opacity="0.6" TextWrapping="Wrap"/>
+        </StackPanel>
+        <ListBox Grid.Row="1" ItemsSource="{Binding Plans}" SelectedItem="{Binding SelectedPlan}">
+          <ListBox.ItemTemplate>
+            <DataTemplate x:DataType="vm:SeatingPlanSummary">
+              <StackPanel Margin="4,6" Spacing="2">
+                <TextBlock Text="{Binding Name}" FontWeight="SemiBold"/>
+                <TextBlock Text="{Binding RoomDisplay}" FontSize="12" Opacity="0.6"/>
+              </StackPanel>
+            </DataTemplate>
+          </ListBox.ItemTemplate>
+        </ListBox>
+        <StackPanel Grid.Row="2" Spacing="8" Margin="0,12,0,0">
+          <Button Content="＋ Sitzplan" Command="{Binding AddPlanCommand}" HorizontalAlignment="Stretch"/>
+          <Grid ColumnDefinitions="*,8,*" IsVisible="{Binding HasSelectedPlan}">
+            <Button Grid.Column="0" Content="Bearbeiten" Command="{Binding EditPlanCommand}"
+                    HorizontalAlignment="Stretch"/>
+            <Button Grid.Column="2" Content="Löschen" Command="{Binding DeletePlanCommand}"
+                    HorizontalAlignment="Stretch"/>
+          </Grid>
+        </StackPanel>
+      </Grid>
+    </Border>
+
+    <Grid Grid.Column="1">
+      <StackPanel HorizontalAlignment="Center" VerticalAlignment="Center" Spacing="10"
+                  IsVisible="{Binding HasPlans, Converter={x:Static BoolConverters.Not}}">
+        <TextBlock Text="Noch kein Sitzplan" FontSize="20" FontWeight="SemiBold"
+                   HorizontalAlignment="Center"/>
+        <TextBlock Text="Lege einen Plan an und ordne die Schüler den Plätzen zu."
+                   Opacity="0.6" TextAlignment="Center"/>
+        <Button Content="Ersten Sitzplan anlegen" Command="{Binding AddPlanCommand}"
+                HorizontalAlignment="Center"/>
+      </StackPanel>
+
+      <Grid RowDefinitions="Auto,*" IsVisible="{Binding HasSelectedPlan}" Margin="24">
+        <Grid Grid.Row="0" ColumnDefinitions="*,Auto" Margin="0,0,0,18">
+          <StackPanel Spacing="3">
+            <TextBlock Text="{Binding PlanTitle}" FontSize="22" FontWeight="SemiBold"/>
+            <TextBlock Text="{Binding PlanSubtitle}" Opacity="0.65"/>
+          </StackPanel>
+          <TextBlock Grid.Column="1" Text="{Binding AssignmentSummary}" VerticalAlignment="Bottom"
+                     FontSize="12" Opacity="0.6"/>
+        </Grid>
+
+        <ScrollViewer Grid.Row="1" HorizontalScrollBarVisibility="Auto"
+                      VerticalScrollBarVisibility="Auto">
+          <StackPanel Spacing="14" HorizontalAlignment="Center">
+            <Border Background="{DynamicResource SystemControlBackgroundChromeMediumLowBrush}"
+                    CornerRadius="6" Padding="36,8" HorizontalAlignment="Center">
+              <TextBlock Text="Tafel / Vorderseite" FontWeight="SemiBold" Opacity="0.75"/>
+            </Border>
+            <ItemsControl ItemsSource="{Binding Seats}" HorizontalAlignment="Center">
+              <ItemsControl.ItemsPanel>
+                <ItemsPanelTemplate>
+                  <UniformGrid Columns="{Binding PlanColumns}"/>
+                </ItemsPanelTemplate>
+              </ItemsControl.ItemsPanel>
+              <ItemsControl.ItemTemplate>
+                <DataTemplate x:DataType="vm:SeatCellViewModel">
+                  <Border Width="190" MinHeight="76" Margin="5" Padding="10"
+                          BorderBrush="{DynamicResource SystemControlForegroundBaseLowBrush}"
+                          BorderThickness="1" CornerRadius="7">
+                    <StackPanel Spacing="5">
+                      <TextBlock Text="{Binding PositionLabel}" FontSize="10" Opacity="0.5"/>
+                      <ComboBox ItemsSource="{Binding Options}" SelectedItem="{Binding SelectedOption}"
+                                IsEnabled="{Binding CanEdit}" HorizontalAlignment="Stretch">
+                        <ComboBox.ItemTemplate>
+                          <DataTemplate x:DataType="vm:StudentSeatOption">
+                            <TextBlock Text="{Binding DisplayName}"/>
+                          </DataTemplate>
+                        </ComboBox.ItemTemplate>
+                      </ComboBox>
+                    </StackPanel>
+                  </Border>
+                </DataTemplate>
+              </ItemsControl.ItemTemplate>
+            </ItemsControl>
+          </StackPanel>
+        </ScrollViewer>
+      </Grid>
+    </Grid>
+  </Grid>
+</UserControl>

LehrerApp.Desktop/Views/Groups/SeatingPlanTabView.axaml.cs

@@ -0,0 +1,46 @@
+using Avalonia.Controls;
+using LehrerApp.Core.Models;
+using LehrerApp.Desktop.ViewModels.Groups;
+using LehrerApp.Desktop.Views.Shared;
+
+namespace LehrerApp.Desktop.Views.Groups;
+
+public partial class SeatingPlanTabView : UserControl
+{
+    public SeatingPlanTabView() => InitializeComponent();
+
+    protected override void OnDataContextChanged(EventArgs e)
+    {
+        base.OnDataContextChanged(e);
+        if (DataContext is SeatingPlanTabViewModel vm)
+        {
+            vm.OnEditPlan = ShowPlanDialog;
+            vm.OnConfirmDelete = ShowDeleteConfirmDialog;
+        }
+    }
+
+    private async Task<SeatingPlan?> ShowPlanDialog(SeatingPlan? plan)
+    {
+        if (DataContext is not SeatingPlanTabViewModel vm) return null;
+        var dialogVm = vm.CreateDialogViewModel(plan);
+        var dialog = new SeatingPlanDialog { DataContext = dialogVm };
+        var owner = TopLevel.GetTopLevel(this) as Window;
+        if (owner is null || !await dialog.ShowDialog<bool>(owner)) return null;
+        return dialogVm.Result;
+    }
+
+    private async Task<bool> ShowDeleteConfirmDialog(SeatingPlanSummary plan)
+    {
+        var dialog = new ConfirmDialog
+        {
+            DataContext = new ConfirmDialogInfo
+            {
+                Title = "Sitzplan löschen?",
+                Message = $"Der Sitzplan „{plan.Name}“ und seine Zuordnungen werden gelöscht.",
+                ConfirmText = "Löschen",
+            },
+        };
+        var owner = TopLevel.GetTopLevel(this) as Window;
+        return owner is not null && await dialog.ShowDialog<bool>(owner);
+    }
+}