fontSize method
Scale font size responsively.
Uses configurable font scale factors (default: mobile 1x, tablet 1.15x, desktop 1.3x). Intentionally uses smaller multipliers than scale to prevent oversized text.
Implementation
double fontSize(double size) {
final config = _config;
if (isDesktop) return size * config.desktopFontScale;
if (isTablet) return size * config.tabletFontScale;
return size * config.mobileFontScale;
}