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.

package.json

@@ -5,6 +5,9 @@
     "test:e2e": "playwright test"
   },
   "devDependencies": {
-    "@playwright/test": "1.59.1"
+    "@playwright/test": "^1.59.1"
+  },
+  "dependencies": {
+    "playwright": "^1.59.1"
   }
-}
+}