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>