feat: add colored top border to stats cards

src/frontend/components/StatsCard.tsx

@@ -14,18 +14,21 @@ interface StatsCardProps {
 }
 
 export function StatsCard({ title, value, description, icon: Icon, color, trend }: StatsCardProps) {
+  const accentColor = `var(--mantine-color-${color ?? 'brand-blue'}-5)`
+
   return (
     <Card
       withBorder
       padding="lg"
       radius="xl"
       className="premium-card"
-      styles={(theme) => ({
+      styles={{
         root: {
           backgroundColor: 'var(--mantine-color-body)',
           borderColor: 'rgba(128,128,128,0.1)',
+          borderTop: `3px solid ${accentColor}`,
         },
-      })}
+      }}
     >
       <Group justify="space-between" mb="xs">
         <ThemeIcon