fix(cabinet): equal-height StatCards so dashboard balance/referral align

In a grid, the wrapping <Link> stretched to the row height but the
StatCard inside only took content height, so the referral card (which has
a subValue line) rendered taller than the balance card ('один толще
другого'). Make StatCard fill its cell with h-full and stretch the
StatsGrid links. Verified by rendering both cards against the built CSS:
balance 86px->94px, now equal to referral's 94px.

src/components/stats/StatCard.tsx

@@ -50,7 +50,7 @@ export function StatCard({
   const trendStyle = delta ? (TREND_STYLES[delta.trend] ?? TREND_STYLES.stable) : null;
 
   return (
-    <div className="rounded-xl bg-dark-800/30 p-3 transition-colors hover:bg-dark-800/50">
+    <div className="h-full rounded-xl bg-dark-800/30 p-3 transition-colors hover:bg-dark-800/50">
       <div className="flex items-center justify-between gap-2">
         <span className="truncate text-xs text-dark-500 sm:text-sm">{label}</span>
         {trailing}