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/Services/Export/SearchCsvExportService.cs

@@ -1,6 +1,7 @@
 using System.IO;
 using System.Text;
 using SharepointToolbox.Core.Models;
+using SharepointToolbox.Localization;
 
 namespace SharepointToolbox.Services.Export;
 
@@ -12,10 +13,11 @@ public class SearchCsvExportService
 {
     public string BuildCsv(IReadOnlyList<SearchResult> results)
     {
+        var T = TranslationSource.Instance;
         var sb = new StringBuilder();
 
         // Header
-        sb.AppendLine("File Name,Extension,Path,Created,Created By,Modified,Modified By,Size (bytes)");
+        sb.AppendLine($"{T["report.col.file_name"]},{T["report.col.extension"]},{T["report.col.path"]},{T["report.col.created"]},{T["report.col.created_by"]},{T["report.col.modified"]},{T["report.col.modified_by"]},{T["report.col.size_bytes"]}");
 
         foreach (var r in results)
         {