Two more device-independent live-path guards: the highlighter tool commits a
PenStrokeKind.highlighter stroke; a single finger PANS the shared transform
(translation changes) when finger-drawing is off and does NOT draw — the
touch→pan vs stylus→draw split.
flutter analyze lib/editor clean; 240/240 tests (+2).
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
