refactor: migrate dashboard components to Design System v4

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

frontend/src/components/dashboard/PerformanceCards.tsx

@@ -71,20 +71,20 @@ export function PerformanceCards() {
           key={card.label}
           onClick={() => navigate(card.href)}
           className={cn(
-            'glass-card p-4 text-left fade-in',
+            'card-interactive p-4 text-left fade-in',
             i === 0 && 'active-glow'
           )}
           style={{ animationDelay: `${400 + i * 60}ms` }}
         >
           <div className="flex items-center justify-between mb-2">
-            <p className="font-label text-[0.5625rem] uppercase tracking-[0.1em] text-muted-foreground">
+            <p className="font-sans text-xs text-[0.5625rem] uppercase tracking-[0.1em] text-[#848b9b]">
               {card.label}
             </p>
             <card.icon size={14} style={{ color: card.iconColor }} />
           </div>
           <p className={cn(
             'font-heading text-2xl font-extrabold tracking-tight',
-            card.highlight ? 'text-gradient-brand' : 'text-foreground'
+            card.highlight ? 'text-[#67e8f9]' : 'text-[#e2e5eb]'
           )}>
             {card.value}
           </p>