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/BulkSitesViewModel.cs

@@ -105,9 +105,9 @@ public partial class BulkSitesViewModel : FeatureViewModelBase
 
     protected override async Task RunOperationAsync(CancellationToken ct, IProgress<OperationProgress> progress)
     {
-        if (_currentProfile == null) throw new InvalidOperationException("No tenant connected.");
+        if (_currentProfile == null) throw new InvalidOperationException(TranslationSource.Instance["err.no_tenant"]);
         if (_validRows == null || _validRows.Count == 0)
-            throw new InvalidOperationException("No valid rows to process. Import a CSV first.");
+            throw new InvalidOperationException(TranslationSource.Instance["err.no_valid_rows"]);
 
         var message = string.Format(TranslationSource.Instance["bulk.confirm.message"],
             $"{_validRows.Count} sites will be created");