feat: add theme mode support with AppThemeMode enum and AppThemeState service

- Introduced AppThemeMode enum to define theme options: System, Light, Dark.
- Updated AppSettingsDocument to include ThemeMode property.
- Created AppThemeState service to manage current theme mode and handle changes.
- Integrated theme mode handling in CouchbaseLiteAppSettingsService for persistence.
- Added JavaScript for theme management in the frontend, supporting system preference detection.
- Enhanced CSS with theme variables for consistent styling across light and dark modes.
- Updated Playwright tests to ensure sidebar functionality and responsiveness.

.gitignore

@@ -1,6 +1,10 @@
 # Build outputs
 bin/
 obj/
+node_modules/
+test-results/
+playwright-report/
+blob-report/
 
 # User-specific files
 *.user
@@ -27,6 +31,8 @@ Data/*.db-*
 *.sqlite3
 App_Data/
 .docker-data/
+probe-desktop.png
+probe-mobile.png
 
 # Secrets and environment files
 .env