resolveFor method
Returns the active column count for a given width. Mobile-first: takes the largest matching breakpoint. Returns null if no configuration is set → "auto" (evenly distributed).
Implementation
int? resolveFor(double width) {
int? result = xs; // Base value (mobile first)
if (width >= BsBreakpoints.sm && sm != null) result = sm;
if (width >= BsBreakpoints.md && md != null) result = md;
if (width >= BsBreakpoints.lg && lg != null) result = lg;
if (width >= BsBreakpoints.xl && xl != null) result = xl;
if (width >= BsBreakpoints.xxl && xxl != null) result = xxl;
return result;
}