fix(charts): widen comparison-baseline buttons to 44 px on mobile

The chart-overlay popover comparison row used `h-9 px-1`, which falls
below the WCAG 2.5.5 floor on touch. Switch to
`min-h-11 sm:min-h-9 px-2` so the mobile button reaches the 44 px
target while desktop keeps the dense 36 px row that fits the popover.

src/components/charts/chart-overlay-controls.tsx

@@ -248,7 +248,7 @@ export function ChartOverlayControlsBody({
                   prefs.comparisonBaseline === value ? "default" : "outline"
                 }
                 size="sm"
-                className={`h-9 px-1 text-[11px] ${isGreyed ? "opacity-50" : ""}`.trim()}
+                className={`min-h-11 sm:min-h-9 px-2 text-[11px] ${isGreyed ? "opacity-50" : ""}`.trim()}
                 onClick={() => setComparisonBaseline(value)}
                 aria-pressed={prefs.comparisonBaseline === value}
                 aria-disabled={isGreyed || undefined}