fix: add missing flutter_driver dependency for BrowserStack Appium integration

Add flutter_driver to dev_dependencies as required by BrowserStack's
Appium Flutter Driver. This resolves the ADB access error by ensuring
the Flutter app has proper driver support for BrowserStack testing.

Required by: https://www.browserstack.com/guide/test-flutter-apps-with-appium

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <[email protected]>

Author: teodorciuraru

flutter_app/pubspec.yaml

@@ -45,6 +45,8 @@ dependencies:
 dev_dependencies:
   flutter_test:
     sdk: flutter
+  flutter_driver:
+    sdk: flutter
   integration_test:
     sdk: flutter