Implement Switch Access traversal order simulation

Use WidgetTester.semantics to get the root SemanticsNode, then walk the tree using SemanticsNode.childrenInTraversalOrder. For 'unreachable' detection, build a directed graph from traversal order and run a reachability check from the root. For 'illogical order' detection, sort nodes by (rect.top, rect.left) and compare against traversal order — flag nodes whose position deviates by more than one position from the sorted baseline. Ensure the wizard screens are pumped with all required BLoC/Riverpod providers before traversal.

Use tester.pumpAndSettle() with a timeout before each traversal capture. Model SwitchAccessTraversalViolation as a freezed data class for immutability and easy JSON serialization. This audit is especially critical for Blindeforbundet and NHF users who rely on switch access due to motor or visual impairments.

Unit tests: verify SwitchAccessTraversalViolation model serializes/deserializes correctly; verify traversal order comparator logic with hand-crafted node trees. Integration tests: run the audit on a real widget tree pumped in flutter_test — assert zero violations on a known-good scaffold, assert expected violations on a deliberately broken scaffold (orphaned node, reversed order). Test coverage target: 90% of traversal enumeration logic. Key scenario: inject a semantics node with no predecessor link and assert it is detected as unreachable.