Add Flutter/Dart CI workflow

[Clancey]

Adds .github/workflows/flutter-ci.yml to run CI on the Dart/Flutter side of the codebase.

Jobs

Job	Command	Working dir
analyze	flutter analyze	flutter_module/
test	flutter test	flutter_module/
format-check	dart format --output=none --set-exit-if-changed	flutter_module/lib/

Triggers

• Push/PR to main when files under flutter_module/, flutter_sharp/, or this workflow change

Notes

• Uses subosito/flutter-action@v2 on the stable channel with pub cache enabled
• Handles the local path dependency (flutter_sharp/) automatically via full repo checkout
• Test job runs against existing flutter_module/test/widget_test.dart