fix(mui): StatCard icon — solid color tile + white glyph (was low-contrast/dark)

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/admin/ui/StatCard.tsx

@@ -30,8 +30,10 @@ export default function StatCard({
   color = "default",
   footer,
 }: StatCardProps) {
-  const iconBg = color === "default" ? "action.hover" : `${color}.light`;
-  const iconColor = color === "default" ? "text.secondary" : `${color}.main`;
+  // Solid tile + white glyph: high-contrast in both themes (the old light tint
+  // left the icon dark/low-visibility, esp. for the default variant).
+  const iconBg = color === "default" ? "grey.600" : `${color}.main`;
+  const iconColor = "common.white";
 
   return (
     <Card>