figure: note same-axis-kind assumption in row y fit

src/plot/figure.cpp

@@ -495,6 +495,7 @@ void Figure::sync_row_y() {
         bounds = any ? Range{std::min(bounds.min, b.min), std::max(bounds.max, b.max)} : b;
         any = true;
       }
+      // The first cell stands in for the row: all cells are assumed to share one y axis kind/padding (the host builds them identically).
       if (any && plots_[first].fit_y_bounds(0u, bounds)) target = plots_[first].y_axis(0u).range;
       // else: nothing to fit -- keep the range the group had
     }