Implement backup and restore functionality; add IBackupService and BackupService; refactor services to use DbContextFactory

src/Duempelkas.App/Pages/Accounts/AccountDetail.razor

@@ -28,6 +28,7 @@
             <button class="btn btn-secondary btn-nav" @onclick="NavigateBack">
                 <i class="bi bi-arrow-left"></i> Zurück
             </button>
+            |
             <button class="btn btn-success btn-nav" @onclick="() => showAddEntry = true">
                 <i class="bi bi-plus-lg"></i> Buchung
             </button>
@@ -37,6 +38,7 @@
             <button class="btn btn-dark btn-nav" @onclick="HandleExport">
                 <i class="bi bi-file-earmark-pdf"></i> PDF
             </button>
+            |
             <button class="btn btn-nav @(showCurrentYearOnly ? "btn-primary" : "btn-outline-secondary")" @onclick="ToggleYearFilter">
                 <i class="bi bi-funnel"></i> @(showCurrentYearOnly ? $"Nur {DateTime.Now.Year}" : "Alle Buchungen")
             </button>

src/Duempelkas.App/Pages/Dashboard.razor

@@ -1,6 +1,9 @@
 @page "/"
 @inject IAccountService AccountService
+@inject IBackupService BackupService
 @inject ISettingsService SettingsService
+@inject IJSRuntime JsRuntime
+@inject NavigationManager NavigationManager
 
 <div class="container-fluid">
 
@@ -19,8 +22,22 @@
         <button class="btn-nav btn-primary" @onclick="() => showAddAccount = true">
             <i class="bi bi-plus-lg"></i> Neues Konto
         </button>
+        |
+        <button class="btn-nav btn-success" @onclick="HandleBackupAsync">
+            <i class="bi bi-save"></i> Backup
+        </button>
+        <button class="btn-nav btn-warning" @onclick="HandleRestoreAsync">
+            <i class="bi bi-arrow-counterclockwise"></i> Restore
+        </button>
     </div>
 
+    @if (!string.IsNullOrWhiteSpace(operationMessage))
+    {
+        <div class="alert @operationMessageClass mb-3" role="alert">
+            @operationMessage
+        </div>
+    }
+
     @if (accounts == null)
     {
         <div class="text-center py-5">
@@ -56,6 +73,8 @@
     private bool showAddAccount;
     private bool showEditClubName;
     private string clubName = string.Empty;
+    private string? operationMessage;
+    private string operationMessageClass = "alert-info";
     private string DisplayClubName => string.IsNullOrWhiteSpace(clubName) ? "Mein Verein" : clubName;
 
     protected override async Task OnInitializedAsync()
@@ -87,4 +106,39 @@
         showEditClubName = false;
         await LoadClubName();
     }
+
+    private async Task HandleBackupAsync()
+    {
+        var message = await BackupService.CreateBackupAsync();
+        if(message.Contains("fehlgeschlagen", StringComparison.OrdinalIgnoreCase)) {
+            SetOperationMessage(message, false);
+        }
+        
+    }
+
+    private async Task HandleRestoreAsync()
+    {
+        var confirmed = await JsRuntime.InvokeAsync<bool>("confirm",
+            "Restore überschreibt die aktuelle Datenbank. Möchten Sie fortfahren?");
+
+        if (!confirmed) return;
+
+        var message = await BackupService.RestoreBackupAsync();
+        var isSuccess = message.StartsWith("Wiederherstellung erfolgreich", StringComparison.OrdinalIgnoreCase);
+
+        if (isSuccess)
+        {
+            // Reload the Blazor app so all components/services re-query from restored DB.
+            NavigationManager.NavigateTo("/", forceLoad: true);
+        } else {
+            SetOperationMessage(message, isSuccess);
+        }
+
+    }
+
+    private void SetOperationMessage(string message, bool success)
+    {
+        operationMessage = message;
+        operationMessageClass = success ? "alert-success" : "alert-danger";
+    }
 }