feat: Formulare-Menü mit Elternbrief-Einstieg + Arbeitsblatt-Personalisierung (Nutzer-Feedback)

Neue Menü-Kategorie "Formulare" in der Menüleiste: "Elternbrief erzeugen..." öffnet
jetzt einen Schüler-Picker statt nur aus der Schülerdetailansicht erreichbar zu sein,
"Arbeitsblatt personalisieren..." ist aktiv, sobald eine einzelne Lerngruppe geöffnet
ist, und erzeugt aus einer in TemplateDesigner gebauten .lavorlage-Vorlage ein PDF je
aktivem Gruppenmitglied - über eine von den Elternbrief-Vorlagen getrennte
WorksheetTemplateStore-Bibliothek.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

LehrerApp.Desktop/Views/Students/StudentDetailView.axaml.cs

@@ -8,7 +8,6 @@ using LehrerApp.Desktop.Services;
 using LehrerApp.Desktop.ViewModels.Students;
 using LehrerApp.Desktop.Views.Shared;
 using Microsoft.Extensions.DependencyInjection;
-using LehrerApp.Templating;
 
 namespace LehrerApp.Desktop.Views.Students;
 
@@ -56,16 +55,7 @@ public partial class StudentDetailView : UserControl
     {
         var owner = TopLevel.GetTopLevel(this) as Window;
         if (owner is null || DataContext is not StudentDetailViewModel { Student: { } student }) return;
-
-        var vm = new CreateLetterDialogViewModel(student,
-            App.Services.GetRequiredService<TemplateStore>(),
-            App.Services.GetRequiredService<ITemplateRenderer>(),
-            App.Services.GetRequiredService<IGroupMembershipRepository>(),
-            App.Services.GetRequiredService<IGroupRepository>());
-        var dialog = new CreateLetterDialog { DataContext = vm };
-        var path = await dialog.ShowDialog<string?>(owner);
-        if (!string.IsNullOrEmpty(path) && File.Exists(path))
-            System.Diagnostics.Process.Start(new System.Diagnostics.ProcessStartInfo(path) { UseShellExecute = true });
+        await LetterDialogs.ShowCreateLetterDialogAsync(owner, student);
     }
 
     private void ShowAddressViewer(ContactItem contact)

LehrerApp.Desktop/Views/Students/StudentPickerDialog.axaml

@@ -0,0 +1,41 @@
+<Window xmlns="https://github.com/avaloniaui"
+        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+        xmlns:vm="clr-namespace:LehrerApp.Desktop.ViewModels.Students"
+        xmlns:vmg="clr-namespace:LehrerApp.Desktop.ViewModels.Groups"
+        x:Class="LehrerApp.Desktop.Views.Students.StudentPickerDialog"
+        x:DataType="vm:StudentPickerDialogViewModel"
+        Title="Schüler wählen"
+        Width="380" Height="480"
+        CanResize="False" WindowStartupLocation="CenterOwner">
+
+  <Grid RowDefinitions="Auto,*,Auto" Margin="24">
+
+    <StackPanel Grid.Row="0" Spacing="12" Margin="0,0,0,12">
+      <TextBlock Text="Schüler wählen" Classes="dialogtitle"/>
+      <TextBox Text="{Binding SearchText}"
+               PlaceholderText="Schüler suchen …"
+               x:Name="SearchBox"/>
+    </StackPanel>
+
+    <ListBox Grid.Row="1"
+             ItemsSource="{Binding Students}"
+             SelectedItem="{Binding SelectedStudent}"
+             BorderThickness="1">
+      <ListBox.ItemTemplate>
+        <DataTemplate x:DataType="vmg:StudentPickerItem">
+          <TextBlock Text="{Binding FullName}" Padding="4,2"/>
+        </DataTemplate>
+      </ListBox.ItemTemplate>
+    </ListBox>
+
+    <StackPanel Grid.Row="2" Spacing="12" Margin="0,16,0,0">
+      <TextBlock Text="{Binding ValidationMessage}" Foreground="Red" FontSize="12"
+                 IsVisible="{Binding ValidationMessage, Converter={x:Static StringConverters.IsNotNullOrEmpty}}"/>
+      <Grid ColumnDefinitions="*,8,*">
+        <Button Grid.Column="0" Content="Abbrechen" HorizontalAlignment="Stretch" Click="OnCancel"/>
+        <Button Grid.Column="2" Content="Weiter" HorizontalAlignment="Stretch" Click="OnSave"/>
+      </Grid>
+    </StackPanel>
+
+  </Grid>
+</Window>

LehrerApp.Desktop/Views/Students/StudentPickerDialog.axaml.cs

@@ -0,0 +1,25 @@
+using Avalonia.Controls;
+using Avalonia.Interactivity;
+using LehrerApp.Desktop.ViewModels.Students;
+
+namespace LehrerApp.Desktop.Views.Students;
+
+public partial class StudentPickerDialog : Window
+{
+    public StudentPickerDialog() => InitializeComponent();
+
+    protected override void OnOpened(EventArgs e)
+    {
+        base.OnOpened(e);
+        this.FindControl<TextBox>("SearchBox")?.Focus();
+    }
+
+    private void OnSave(object? sender, RoutedEventArgs e)
+    {
+        if (DataContext is not StudentPickerDialogViewModel vm) return;
+        vm.SelectCommand.Execute(null);
+        if (vm.Result is not null) Close(vm.Result);
+    }
+
+    private void OnCancel(object? sender, RoutedEventArgs e) => Close(null);
+}