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>

.editorconfig

@@ -0,0 +1,16 @@
+root = true
+
+[*.cs]
+indent_style = space
+indent_size = 4
+end_of_line = crlf
+charset = utf-8
+trim_trailing_whitespace = true
+insert_final_newline = true
+
+# ConfigureAwait(false) is required in non-UI service/infrastructure code so
+# callers that may still sync-wait cannot deadlock on the WPF dispatcher.
+# Scoped to Services/ and Infrastructure/ — ViewModels legitimately resume on
+# the UI thread for INotifyPropertyChanged updates.
+[{SharepointToolbox/Services/**.cs,SharepointToolbox/Infrastructure/**.cs}]
+dotnet_diagnostic.CA2007.severity = suggestion