chore: release v2.4

- Add theme system (Dark/Light palettes, ModernTheme, ThemeManager)
- Add InputDialog, Spinner common view
- Add DuplicatesCsvExportService
- Refresh views, dialogs, and view models across tabs
- Update localization strings (en/fr)
- Tweak services (transfer, permissions, search, user access, ownership elevation, bulk operations)

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

SharepointToolbox/ViewModels/Tabs/FolderStructureViewModel.cs

@@ -103,15 +103,16 @@ public partial class FolderStructureViewModel : FeatureViewModelBase
 
     protected override async Task RunOperationAsync(CancellationToken ct, IProgress<OperationProgress> progress)
     {
-        if (_currentProfile == null) throw new InvalidOperationException("No tenant connected.");
+        var T = TranslationSource.Instance;
+        if (_currentProfile == null) throw new InvalidOperationException(T["err.no_tenant"]);
         if (_validRows == null || _validRows.Count == 0)
-            throw new InvalidOperationException("No valid rows. Import a CSV first.");
+            throw new InvalidOperationException(T["err.no_valid_rows"]);
         if (string.IsNullOrWhiteSpace(LibraryTitle))
-            throw new InvalidOperationException("Library title is required.");
+            throw new InvalidOperationException(T["err.library_title_required"]);
 
         var urls = GlobalSites.Select(s => s.Url).Where(u => !string.IsNullOrWhiteSpace(u)).ToList();
         if (urls.Count == 0)
-            throw new InvalidOperationException("Select at least one site from the toolbar.");
+            throw new InvalidOperationException(T["err.no_sites_selected"]);
 
         var uniquePaths = FolderStructureService.BuildUniquePaths(_validRows);
         var message = string.Format(TranslationSource.Instance["bulk.confirm.message"],