Notenschlüssel-Editor (1.3) und Einstellungen in Tabs strukturiert

- Notenschlüssel-Editor im ExamDialog: Stufen (Note/Prozentgrenze)
  bearbeitbar, Vorbelegung passend zum GradingSystem der Gruppe,
  Live-Anzeige der absoluten Punktegrenze je Stufe, Validierung
  (lückenlos, keine Dopplungen) über GradingService.ValidateGradingKey.
- Neues Modell GradingKeyTemplate + Repository: Notenschlüssel als
  Vorlage speichern/anwenden, direkt aus dem ExamDialog heraus.
- Einstellungen: Fächer / Kompetenzen / Notenschlüssel-Vorlagen sind
  jetzt eigene Tabs statt einer gemeinsam wachsenden Liste. Vorlagen
  zeigen nur noch eine kompakte Zeile; die Stufen-Bearbeitung läuft
  über ein Popup-Fenster (GradingKeyTemplateDialog).

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

LehrerApp.Desktop/ViewModels/Groups/ExamViewModels.cs

@@ -14,11 +14,13 @@ public partial class ExamDialogViewModel : ObservableObject
 {
     private readonly IExamRepository _exams;
     private readonly ICompetencyDomainRepository _competencyDomains;
+    private readonly IGradingKeyTemplateRepository _gradingKeyTemplates;
+    private readonly GradingService _grading;
     private readonly Guid _groupId;
     private readonly Guid? _subjectId;
     private readonly int _gradeLevel;
+    private readonly GradingSystem _gradingSystem;
     private readonly Exam? _editingExam;
-    private readonly List<GradingKeyEntry> _gradingKey;
     private readonly string _subjectName;
 
     [ObservableProperty] private string _title = "";
@@ -30,12 +32,17 @@ public partial class ExamDialogViewModel : ObservableObject
     [ObservableProperty] private double _totalPoints;
     [ObservableProperty] private bool _hasCompetencyCatalog;
     [ObservableProperty] private bool _useWeighting;
+    [ObservableProperty] private GradingKeyTemplate? _selectedTemplate;
+    [ObservableProperty] private string _newTemplateName = "";
+    [ObservableProperty] private string _gradingKeyValidation = "";
 
     public bool TotalPointsWarning => TotalPoints <= 0;
     public string TotalPointsDisplay =>
         $"{TotalPoints.ToString("0.##", CultureInfo.InvariantCulture)} Punkte gesamt";
 
     public ObservableCollection<ExamTaskEditItem> Tasks { get; } = [];
+    public ObservableCollection<GradingKeyEntryEditItem> GradingKeyEntries { get; } = [];
+    public ObservableCollection<GradingKeyTemplate> AvailableTemplates { get; } = [];
 
     public Exam? Result { get; private set; }
     public string DialogTitle => _editingExam is null ? "Neue Klausur anlegen" : "Klausur bearbeiten";
@@ -46,17 +53,23 @@ public partial class ExamDialogViewModel : ObservableObject
         ? "Kein Fach hinterlegt (siehe Lerngruppe)" : $"Fach: {_subjectName}";
 
     public ExamDialogViewModel(IExamRepository exams, ICompetencyDomainRepository competencyDomains,
+        IGradingKeyTemplateRepository gradingKeyTemplates, GradingService grading,
         Guid groupId, Guid? subjectId, int gradeLevel, GradingSystem gradingSystem,
         string defaultSubjectName, Exam? editingExam, Exam? duplicateSource)
     {
         _exams = exams; _competencyDomains = competencyDomains;
+        _gradingKeyTemplates = gradingKeyTemplates; _grading = grading;
         _groupId = groupId; _subjectId = subjectId; _gradeLevel = gradeLevel;
+        _gradingSystem = gradingSystem;
         _editingExam = editingExam;
         _subjectName = defaultSubjectName;
 
         HasCompetencyCatalog = subjectId.HasValue
             && _competencyDomains.GetBySubjectAndGrade(subjectId.Value, gradeLevel).Count > 0;
 
+        foreach (var t in _gradingKeyTemplates.GetByGradingSystem(gradingSystem))
+            AvailableTemplates.Add(t);
+
         var source = editingExam ?? duplicateSource;
         if (source is not null)
         {
@@ -68,16 +81,18 @@ public partial class ExamDialogViewModel : ObservableObject
             ExamNumber = source.ExamNumber;
             Notes      = source.Notes ?? "";
             ReturnedAtText = isDuplicate ? "" : source.ReturnedAt?.ToString("dd.MM.yyyy") ?? "";
-            _gradingKey = source.GradingKey
-                .Select(k => new GradingKeyEntry { Grade = k.Grade, MinPercent = k.MinPercent }).ToList();
             foreach (var t in source.Tasks.OrderBy(t => t.Nr))
                 AddTaskInternal(t.Title, t.MaxPoints, t.Weight, [.. t.CompetencyCodes]);
             UseWeighting = Tasks.Any(t => Math.Abs(t.Weight - 1.0) > 0.0001);
+            foreach (var e in source.GradingKey.OrderByDescending(e => e.MinPercent))
+                AddGradingKeyRowInternal(e.Grade, e.MinPercent);
         }
         else
         {
-            _gradingKey = gradingSystem == GradingSystem.Grades1To6
+            var defaults = gradingSystem == GradingSystem.Grades1To6
                 ? GradingService.DefaultKey1To6() : GradingService.DefaultKey0To15();
+            foreach (var e in defaults)
+                AddGradingKeyRowInternal(e.Grade, e.MinPercent);
         }
         foreach (var t in Tasks) t.ShowWeight = UseWeighting;
         RecomputeTotals();
@@ -158,8 +173,86 @@ public partial class ExamDialogViewModel : ObservableObject
         TotalPoints = Tasks.Sum(t => t.MaxPoints);
         OnPropertyChanged(nameof(TotalPointsWarning));
         OnPropertyChanged(nameof(TotalPointsDisplay));
+        RecomputeGradingKeyAbsolutes();
     }
 
+    // ── Notenschlüssel (1.3) ──────────────────────────────────────────────────
+
+    private void RecomputeGradingKeyAbsolutes()
+    {
+        foreach (var e in GradingKeyEntries)
+            e.AbsolutePointsDisplay = TotalPoints <= 0
+                ? "–"
+                : $"ab {(e.MinPercent / 100.0 * TotalPoints).ToString("0.##", CultureInfo.InvariantCulture)} " +
+                  $"von {TotalPoints.ToString("0.##", CultureInfo.InvariantCulture)} Punkten";
+    }
+
+    [RelayCommand]
+    private void AddGradingKeyRow()
+    {
+        AddGradingKeyRowInternal("", 0);
+        RecomputeGradingKeyAbsolutes();
+    }
+
+    private void AddGradingKeyRowInternal(string grade, double minPercent)
+    {
+        var item = new GradingKeyEntryEditItem
+        {
+            Grade = grade,
+            MinPercent = minPercent,
+            OnChanged = RecomputeGradingKeyAbsolutes,
+            OnRemove = RemoveGradingKeyRow,
+        };
+        GradingKeyEntries.Add(item);
+    }
+
+    private void RemoveGradingKeyRow(GradingKeyEntryEditItem item)
+    {
+        GradingKeyEntries.Remove(item);
+        RecomputeGradingKeyAbsolutes();
+    }
+
+    [RelayCommand(CanExecute = nameof(HasSelectedTemplate))]
+    private void ApplyTemplate()
+    {
+        if (SelectedTemplate is null) return;
+        GradingKeyEntries.Clear();
+        foreach (var e in SelectedTemplate.Entries.OrderByDescending(x => x.MinPercent))
+            AddGradingKeyRowInternal(e.Grade, e.MinPercent);
+        RecomputeGradingKeyAbsolutes();
+        GradingKeyValidation = "";
+    }
+
+    private bool HasSelectedTemplate() => SelectedTemplate is not null;
+
+    partial void OnSelectedTemplateChanged(GradingKeyTemplate? value) => ApplyTemplateCommand.NotifyCanExecuteChanged();
+
+    [RelayCommand]
+    private void SaveAsTemplate()
+    {
+        if (string.IsNullOrWhiteSpace(NewTemplateName)) { GradingKeyValidation = "Vorlagenname erforderlich."; return; }
+
+        var entries = BuildGradingKeyEntries();
+        var error = _grading.ValidateGradingKey(entries);
+        if (error is not null) { GradingKeyValidation = error; return; }
+
+        var template = new GradingKeyTemplate
+        {
+            Name = NewTemplateName.Trim(),
+            GradingSystem = _gradingSystem,
+            Entries = entries,
+        };
+        _gradingKeyTemplates.Save(template);
+        AvailableTemplates.Add(template);
+        NewTemplateName = "";
+        GradingKeyValidation = "";
+    }
+
+    private List<GradingKeyEntry> BuildGradingKeyEntries() => GradingKeyEntries
+        .Select(e => new GradingKeyEntry { Grade = e.Grade.Trim(), MinPercent = e.MinPercent })
+        .OrderByDescending(e => e.MinPercent)
+        .ToList();
+
     [RelayCommand]
     private void Save()
     {
@@ -180,6 +273,11 @@ public partial class ExamDialogViewModel : ObservableObject
             returnedAt = r;
         }
 
+        var gradingKey = BuildGradingKeyEntries();
+        var gradingKeyError = _grading.ValidateGradingKey(gradingKey);
+        if (gradingKeyError is not null) { GradingKeyValidation = gradingKeyError; return; }
+        GradingKeyValidation = "";
+
         Result = _editingExam ?? new Exam { GroupId = _groupId };
         Result.Title      = Title.Trim();
         Result.Date       = date;
@@ -188,11 +286,28 @@ public partial class ExamDialogViewModel : ObservableObject
         Result.Notes      = string.IsNullOrWhiteSpace(Notes) ? null : Notes.Trim();
         Result.ReturnedAt = returnedAt;
         Result.Tasks      = Tasks.Select(t => t.ToModel()).ToList();
-        Result.GradingKey = _gradingKey;
+        Result.GradingKey = gradingKey;
         _exams.Save(Result);
     }
 }
 
+// ── Zeile im Notenschlüssel-Editor (1.3) ──────────────────────────────────────
+
+public partial class GradingKeyEntryEditItem : ObservableObject
+{
+    [ObservableProperty] private string _grade = "";
+    [ObservableProperty] private double _minPercent;
+    [ObservableProperty] private string _absolutePointsDisplay = "";
+
+    public Action? OnChanged { get; set; }
+    public Action<GradingKeyEntryEditItem>? OnRemove { get; set; }
+
+    partial void OnMinPercentChanged(double value) => OnChanged?.Invoke();
+    partial void OnGradeChanged(string value) => OnChanged?.Invoke();
+
+    [RelayCommand] private void Remove() => OnRemove?.Invoke(this);
+}
+
 // ── Zeile im Aufgaben-Editor (1.2.1 / 1.2.2 / 1.2.4) ─────────────────────────
 
 public partial class ExamTaskEditItem : ObservableObject