feat: lokaler MCP-Server, Phase 4 (Elternbrief-Vorlagen + Claude-Desktop-Registrierung)

Schließt die MCP-Server-Spec ab. "Worksheets" aus der Spec entsprechen
im tatsächlichen Datenmodell den .lavorlage-Elternbrief-Vorlagen
(LehrerApp.Templating) - es gibt kein separates Arbeitsblatt-Konzept mit
Fach/Klassenstufe-Metadaten. Neue Tools list_letter_templates (Read) und
render_letter (Read, liefert Base64-PDF, kein DB-Schreibzugriff).

upload_worksheet/update_worksheet bewusst nicht umgesetzt: das
Seitenlayout ist eine eigene positionsbasierte DSL mit eigenem
visuellen Editor (LehrerApp.TemplateDesigner) - ein LLM müsste sie
blind erzeugen, mit hohem Risiko für kaputte Layouts. Platzhalter-Logik
aus CreateLetterDialogViewModel nach LetterPlaceholderBuilder extrahiert,
damit Dialog und MCP-Tool nicht auseinanderdriften.

Neuer McpClientRegistrationService trägt den Bridge-Pfad in Claude
Desktops claude_desktop_config.json ein (Button in den Einstellungen,
nie automatisch), ohne bestehende Fremdeinträge zu verlieren und ohne
eine nicht lesbare Konfigurationsdatei zu überschreiben.

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

LehrerApp.Desktop/ViewModels/Settings/SettingsViewModel.McpSettings.cs

@@ -1,5 +1,7 @@
 using CommunityToolkit.Mvvm.ComponentModel;
+using CommunityToolkit.Mvvm.Input;
 using LehrerApp.Desktop.Services;
+using LehrerApp.Desktop.Services.Mcp;
 
 namespace LehrerApp.Desktop.ViewModels.Settings;
 
@@ -14,4 +16,27 @@ public partial class SettingsViewModel
     // Kein Live-Reload (siehe McpServerHostedService/Planungsdokument) - der Pipe-Listener wird
     // nur beim App-Start eingerichtet, deshalb wirkt eine Änderung hier erst nach Neustart.
     partial void OnMcpEnabledChanged(bool value) => _mcpSettings.SetEnabled(value);
+
+    // ── MCP: Registrierung bei Claude Desktop ─────────────────────────────────
+
+    [ObservableProperty] private string _mcpRegistrationStatus = "";
+    [ObservableProperty] private bool _mcpIsRegisteredWithClaude;
+
+    private void LoadMcpRegistrationStatus() => McpIsRegisteredWithClaude = _mcpRegistration.IsRegistered();
+
+    [RelayCommand]
+    private void RegisterWithClaudeDesktop()
+    {
+        var result = _mcpRegistration.Register();
+        McpRegistrationStatus = result.Message;
+        McpIsRegisteredWithClaude = _mcpRegistration.IsRegistered();
+    }
+
+    [RelayCommand]
+    private void UnregisterFromClaudeDesktop()
+    {
+        var result = _mcpRegistration.Unregister();
+        McpRegistrationStatus = result.Message;
+        McpIsRegisteredWithClaude = _mcpRegistration.IsRegistered();
+    }
 }

LehrerApp.Desktop/ViewModels/Settings/SettingsViewModel.cs

@@ -75,6 +75,7 @@ public partial class SettingsViewModel : ObservableObject
     private readonly AiSettingsService _aiSettings;
     private readonly AiPlanningService _aiPlanning;
     private readonly McpSettingsService _mcpSettings;
+    private readonly Services.Mcp.McpClientRegistrationService _mcpRegistration;
     private readonly WebUntisSettingsService _untisSettings;
     private readonly WebUntisIntegrationService? _untisIntegration;
     private readonly UntisSyncService? _untisSync;
@@ -102,6 +103,7 @@ public partial class SettingsViewModel : ObservableObject
         SchoolCalendarSettingsService calendarSettings, PeriodScheduleService periodSchedule,
         ISupervisionDutyRepository supervisionDuties, TemplateStore letterTemplates,
         AiSettingsService aiSettings, AiPlanningService aiPlanning, McpSettingsService mcpSettings,
+        Services.Mcp.McpClientRegistrationService mcpRegistration,
         WebUntisSettingsService untisSettings,
         AnnualPlanSettingsService annualPlanSettings,
         SyncSettingsService syncSettings, SyncAuthService syncAuth, EventQueue eventQueue,
@@ -140,6 +142,7 @@ public partial class SettingsViewModel : ObservableObject
         _aiSettings = aiSettings;
         _aiPlanning = aiPlanning;
         _mcpSettings = mcpSettings;
+        _mcpRegistration = mcpRegistration;
         _untisSettings = untisSettings;
         _untisIntegration = untisIntegration;
         _untisSync = untisSync;
@@ -168,6 +171,7 @@ public partial class SettingsViewModel : ObservableObject
         LoadLetterTemplates();
         LoadAiSettings();
         LoadMcpSettings();
+        LoadMcpRegistrationStatus();
         LoadUntisSettings();
         LoadAnnualPlanSettings();
         LoadSyncSettings();

LehrerApp.Desktop/ViewModels/Students/CreateLetterDialogViewModel.cs

@@ -1,6 +1,7 @@
 using CommunityToolkit.Mvvm.ComponentModel;
 using LehrerApp.Core.Interfaces;
 using LehrerApp.Core.Models;
+using LehrerApp.Desktop.Services;
 using LehrerApp.Templating;
 using System.Collections.ObjectModel;
 
@@ -88,27 +89,11 @@ public partial class CreateLetterDialogViewModel : ObservableObject
         OnPropertyChanged(nameof(HasIssues));
     }
 
-    private IReadOnlyDictionary<string, PlaceholderValue> BuildValues()
-    {
-        var contact = SelectedContact?.Model; var group = SelectedGroup?.Model;
-        var cityLine = string.Join(" ", new[] { contact?.PostalCode, contact?.City }.Where(x => !string.IsNullOrWhiteSpace(x)));
-        var address = string.Join(Environment.NewLine, new[] { contact?.Name, contact?.Street, cityLine }.Where(x => !string.IsNullOrWhiteSpace(x)));
-        var date = DateOnly.FromDateTime((LetterDate ?? DateTimeOffset.Now).LocalDateTime);
-        return new Dictionary<string, PlaceholderValue>(StringComparer.Ordinal)
-        {
-            ["Datum"] = new DateValue(date), ["CurrentDate"] = new DateValue(date),
-            ["Empfaenger"] = new TextValue(contact?.Name ?? ""), ["Anrede"] = new TextValue(contact?.LetterSalutation ?? ""),
-            ["Brieftext"] = new MultilineValue(LetterText), ["LehrerName"] = new TextValue(TeacherName),
-            ["Student.FirstName"] = new TextValue(_student.FirstName), ["Student.LastName"] = new TextValue(_student.LastName),
-            ["Contact.Name"] = new TextValue(contact?.Name ?? ""), ["Contact.Address"] = new MultilineValue(address),
-            ["Contact.Street"] = new TextValue(contact?.Street ?? ""), ["Contact.PostalCode"] = new TextValue(contact?.PostalCode ?? ""),
-            ["Contact.City"] = new TextValue(contact?.City ?? ""), ["Letter.Salutation"] = new TextValue(contact?.LetterSalutation ?? ""),
-            ["Group.Name"] = new TextValue(group?.Name ?? ""), ["SchoolYear"] = new TextValue(group?.SchoolYear ?? ""),
-        };
-    }
+    private IReadOnlyDictionary<string, PlaceholderValue> BuildValues() => LetterPlaceholderBuilder.BuildStandardValues(
+        _student, SelectedContact?.Model, SelectedGroup?.Model,
+        DateOnly.FromDateTime((LetterDate ?? DateTimeOffset.Now).LocalDateTime), LetterText, TeacherName);
 
-    private static bool IsEmpty(PlaceholderValue value) => value switch
-    { TextValue x => string.IsNullOrWhiteSpace(x.Value), MultilineValue x => string.IsNullOrWhiteSpace(x.Value), _ => false };
+    private static bool IsEmpty(PlaceholderValue value) => LetterPlaceholderBuilder.IsEmpty(value);
     private static string SanitizeFileName(string value)
     { foreach (var character in Path.GetInvalidFileNameChars()) value = value.Replace(character, '_'); return value; }
 }