Arbeitszeit: wiederkehrende Aufgaben + Auto-Aufgabe bei Klausurkorrektur (6.1.4/6.1.5)

Damit ist Kapitel 6 (Arbeitszeit & Aufgaben) vollständig abgeschlossen (bis auf den
Export der Auswertung, der an das noch fehlende Kapitel 11 hängt).

- WorkTask.Recurrence (None/Weekly/Monthly): beim Abschließen einer wiederkehrenden
  Aufgabe wird automatisch die nächste Instanz mit verschobenem Fälligkeitsdatum erzeugt.
- GroupDetailViewModel.SetExamStatus legt beim ersten Wechsel einer Klausur von
  "Geplant" auf "Durchgeführt" automatisch eine Korrektur-Aufgabe an.

LehrerApp.Desktop.Tests/GroupDetailViewModelTests.cs

@@ -0,0 +1,72 @@
+using LehrerApp.Core.Models;
+using LehrerApp.Core.Services;
+using LehrerApp.Desktop.ViewModels.Groups;
+using Xunit;
+
+namespace LehrerApp.Desktop.Tests;
+
+public sealed class GroupDetailViewModelTests
+{
+    private static (GroupDetailViewModel Vm, FakeExams Exams, FakeWorkTasks Tasks) Build(LearningGroup group, Exam exam)
+    {
+        var exams = new FakeExams([exam]);
+        var tasks = new FakeWorkTasks();
+        var groups = new FakeGroups([group]);
+        var students = new FakeStudents([]);
+        var memberships = new FakeMemberships([]);
+        var subjects = new FakeSubjects([]);
+        var grades = new FakeGrades();
+
+        var vm = new GroupDetailViewModel(groups, students, memberships, subjects, exams, grades, tasks,
+            new ParticipationTabViewModel(new FakeSessions([]), new FakeEntries(), new FakeAspects(),
+                students, memberships, groups, new FakeCompetencyDomains()),
+            new GradeOverviewTabViewModel(grades, exams, new FakeResults(), students, memberships, new GradingService()),
+            new PlanningTabViewModel(new FakeUnits(), new FakeLessons(), groups, subjects, new FakeCompetencyDomains()));
+
+        vm.LoadGroup(group.Id);
+        vm.SelectedExam = vm.Exams.First(e => e.Id == exam.Id);
+        return (vm, exams, tasks);
+    }
+
+    [Fact]
+    public void SetExamStatus_PlannedZuConducted_ErstelltKorrekturAufgabe()
+    {
+        var group = new LearningGroup { Name = "8a", SchoolYear = "2025/26" };
+        var exam = new Exam { GroupId = group.Id, Title = "Klausur 1", Date = new DateOnly(2026, 3, 10) };
+        var (vm, _, tasks) = Build(group, exam);
+
+        vm.SetExamStatusCommand.Execute(ExamStatus.Conducted);
+
+        var task = Assert.Single(tasks.GetAll());
+        Assert.Equal("Klausur korrigieren: Klausur 1", task.Title);
+        Assert.Equal(TaskCategory.Correction, task.Category);
+        Assert.Equal(group.Id, task.GroupId);
+        Assert.Equal(new DateOnly(2026, 3, 24), task.DueDate);
+    }
+
+    [Fact]
+    public void SetExamStatus_ConductedErneutGesetzt_ErstelltKeineZweiteAufgabe()
+    {
+        var group = new LearningGroup { Name = "8a", SchoolYear = "2025/26" };
+        var exam = new Exam { GroupId = group.Id, Title = "Klausur 1", Date = new DateOnly(2026, 3, 10) };
+        var (vm, _, tasks) = Build(group, exam);
+
+        vm.SetExamStatusCommand.Execute(ExamStatus.Conducted);
+        vm.SelectedExam = vm.Exams.First(e => e.Id == exam.Id);
+        vm.SetExamStatusCommand.Execute(ExamStatus.Conducted);
+
+        Assert.Single(tasks.GetAll());
+    }
+
+    [Fact]
+    public void SetExamStatus_DirektAufGraded_ErstelltKeineAufgabe()
+    {
+        var group = new LearningGroup { Name = "8a", SchoolYear = "2025/26" };
+        var exam = new Exam { GroupId = group.Id, Title = "Klausur 1", Date = new DateOnly(2026, 3, 10) };
+        var (vm, _, tasks) = Build(group, exam);
+
+        vm.SetExamStatusCommand.Execute(ExamStatus.Graded);
+
+        Assert.Empty(tasks.GetAll());
+    }
+}

LehrerApp.Desktop.Tests/WorkloadViewModelTests.cs

@@ -93,6 +93,66 @@ public sealed class WorkTaskListViewModelTests
         Assert.Equal(WorkTaskStatus.Open, vm.Tasks[0].Model.Status);
     }
 
+    [Fact]
+    public void CycleStatus_WoechentlicheWiederholungAufErledigt_ErzeugtNaechsteInstanz()
+    {
+        var tasks = new FakeWorkTasks();
+        tasks.Add(new WorkTask
+        {
+            Title = "Wochenbericht", Status = WorkTaskStatus.InProgress,
+            Recurrence = TaskRecurrence.Weekly, DueDate = new DateOnly(2026, 3, 10),
+            Category = TaskCategory.Admin,
+        });
+        var vm = new WorkTaskListViewModel(tasks, new FakeGroups([]), new FakeTimeEntries())
+        {
+            StatusFilter = WorkTaskListViewModel.AllFilter,
+        };
+
+        vm.CycleStatusCommand.Execute(vm.Tasks[0]); // -> Done
+
+        var all = tasks.GetAll();
+        Assert.Equal(2, all.Count);
+        var next = all.Single(t => t.Status == WorkTaskStatus.Open);
+        Assert.Equal("Wochenbericht", next.Title);
+        Assert.Equal(new DateOnly(2026, 3, 17), next.DueDate);
+        Assert.Equal(TaskRecurrence.Weekly, next.Recurrence);
+    }
+
+    [Fact]
+    public void CycleStatus_MonatlicheWiederholung_AddiertEinenMonat()
+    {
+        var tasks = new FakeWorkTasks();
+        tasks.Add(new WorkTask
+        {
+            Title = "Bericht", Status = WorkTaskStatus.InProgress,
+            Recurrence = TaskRecurrence.Monthly, DueDate = new DateOnly(2026, 3, 10),
+        });
+        var vm = new WorkTaskListViewModel(tasks, new FakeGroups([]), new FakeTimeEntries())
+        {
+            StatusFilter = WorkTaskListViewModel.AllFilter,
+        };
+
+        vm.CycleStatusCommand.Execute(vm.Tasks[0]); // -> Done
+
+        var next = tasks.GetAll().Single(t => t.Status == WorkTaskStatus.Open);
+        Assert.Equal(new DateOnly(2026, 4, 10), next.DueDate);
+    }
+
+    [Fact]
+    public void CycleStatus_OhneWiederholung_ErzeugtKeineNeueAufgabe()
+    {
+        var tasks = new FakeWorkTasks();
+        tasks.Add(new WorkTask { Title = "T", Status = WorkTaskStatus.InProgress });
+        var vm = new WorkTaskListViewModel(tasks, new FakeGroups([]), new FakeTimeEntries())
+        {
+            StatusFilter = WorkTaskListViewModel.AllFilter,
+        };
+
+        vm.CycleStatusCommand.Execute(vm.Tasks[0]); // -> Done
+
+        Assert.Single(tasks.GetAll());
+    }
+
     [Fact]
     public void DeleteTask_EntferntAufgabeAusDerListe()
     {
@@ -193,6 +253,37 @@ public sealed class AddEditWorkTaskDialogViewModelTests
         Assert.Equal(source.Id, vm.Result!.Id);
         Assert.Equal(WorkTaskStatus.InProgress, vm.Result.Status);
     }
+
+    [Fact]
+    public void Save_WiederholungOhneFaelligkeitsdatum_SetztFehler()
+    {
+        var vm = new AddEditWorkTaskDialogViewModel(null, [])
+        {
+            Title = "T",
+            SelectedRecurrence = TaskRecurrenceDisplay.Label(TaskRecurrence.Weekly),
+        };
+
+        vm.SaveCommand.Execute(null);
+
+        Assert.Null(vm.Result);
+        Assert.NotEmpty(vm.DueDateError);
+    }
+
+    [Fact]
+    public void Save_WiederholungMitFaelligkeitsdatum_UebernimmtRecurrence()
+    {
+        var vm = new AddEditWorkTaskDialogViewModel(null, [])
+        {
+            Title = "T",
+            DueDateText = "10.03.2026",
+            SelectedRecurrence = TaskRecurrenceDisplay.Label(TaskRecurrence.Monthly),
+        };
+
+        vm.SaveCommand.Execute(null);
+
+        Assert.NotNull(vm.Result);
+        Assert.Equal(TaskRecurrence.Monthly, vm.Result!.Recurrence);
+    }
 }
 
 public sealed class TimeTrackingViewModelTests