Set up audit runner test harness scaffold

Place AccessibilityAuditRunner in integration_test/helpers/accessibility_audit_runner.dart to keep it clearly separated from production code. Use IntegrationTestWidgetsFlutterBinding.ensureInitialized() in the test entry point. Define AuditResult as an @immutable class or record (Dart 3 records are acceptable if the project targets Dart 3+). The runAll() signature should accept WidgetTester to allow future audit steps to pump widgets and interact with SemanticsController.

Add a TODO comment in runAll() body listing the checks to be added in subsequent tasks (modal close, back control, horizontal swipe, semantics labels) so the intended scope is clear to whoever implements those tasks. Confirm with the team that integration_test/ is excluded from the production build pipeline — standard Flutter project setup does this automatically, but CI pipelines with custom build steps may need an explicit exclusion.

Verification via `flutter test` and `flutter analyze`. Confirm: (1) `flutter test integration_test/accessibility_audit_test.dart` exits with code 0, (2) `flutter analyze` reports zero new issues after scaffold addition, (3) `grep -r 'AccessibilityAuditRunner' lib/` returns zero matches confirming no production references, (4) `flutter build apk --release` (or iOS equivalent) succeeds and binary size does not increase vs baseline — confirming zero production footprint. No functional unit tests needed for the scaffold itself — the scaffold's purpose is to be a stable base for subsequent test tasks.