Update flutter_lints to 6.0.0 and fix widget tests

- Upgrade flutter_lints from 5.0.0 to 6.0.0
- Fix widget test to reference correct app class (ArcheryBookkeeperApp)
- Update widget test to check for actual app title "Archery Scoring"
- Clean up project description in pubspec.yaml

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

Co-Authored-By: Claude <noreply@anthropic.com>

pubspec.yaml

@@ -1,5 +1,5 @@
 name: archery_bookkeeper
-description: "A new Flutter project."
+description: "Archery scoring companion."
 # The following line prevents the package from being accidentally published to
 # pub.dev using `flutter pub publish`. This is preferred for private packages.
 publish_to: 'none' # Remove this line if you wish to publish to pub.dev
@@ -44,7 +44,7 @@ dev_dependencies:
   # activated in the `analysis_options.yaml` file located at the root of your
   # package. See that file for information about deactivating specific lint
   # rules and activating additional ones.
-  flutter_lints: ^5.0.0
+  flutter_lints: ^6.0.0
 
 # For information on the generic Dart part of this file, see the
 # following page: https://dart.dev/tools/pub/pubspec