highlightProperties method
Highlight specific properties (update their opacity)
Implementation
void highlightProperties(Set<String> propertyIds) {
_positions = _positions.map((pos) {
final isHighlighted = propertyIds.isEmpty || propertyIds.contains(pos.propertyId);
return pos.copyWith(opacity: isHighlighted ? 1.0 : 0.3);
}).toList();
notifyListeners();
}