eliminate unnecessary code

Remove redundant code constructs and prefer concise, direct patterns that improve readability and maintainability. This includes eliminating unnecessary widget/layout creation, using ternary operators for simple conditionals, direct initialization patterns, and simplifying complex calculations with named constants.

Examples of improvements:

• Instead of creating wrapper widgets unnecessarily: routes_type_selector_->addTab(preserved_route_list_ = new RouteListWidget, tr("&Preserved"));
• Use ternary operators for simple conditionals: return routes_type_selector_->currentIndex() == 0 ? route_list_ : preserved_route_list_;
• Direct layout attachment: auto layout = new QVBoxLayout(widget) instead of separate setLayout() calls
• Replace complex calculations with named constants: const QColor ENGAGED_COLOR = QColor::fromRgbF(0.1, 0.945, 0.26); instead of inline math
• Eliminate unnecessary variable assignments and prefer direct initialization where possible

This approach reduces code bloat, makes intent clearer, and improves maintainability by removing opportunities for errors in redundant code paths.