feat: 브랜드 컬러 토큰 적용 및 색상 규칙 추가

features/layout/components/header.tsx

@@ -38,7 +38,7 @@ export function Header({ user, showDashboardLink = false }: HeaderProps) {
         {/* ========== 좌측: 로고 영역 ========== */}
         <Link href={AUTH_ROUTES.HOME} className="flex items-center gap-2 group">
           <div className="flex h-9 w-9 items-center justify-center rounded-xl bg-primary/10 transition-transform duration-200 group-hover:scale-110">
-            <div className="h-5 w-5 rounded-lg bg-linear-to-br from-indigo-500 to-purple-600" />
+            <div className="h-5 w-5 rounded-lg bg-linear-to-br from-brand-500 to-brand-700" />
           </div>
           <span className="text-xl font-bold tracking-tight text-foreground transition-colors group-hover:text-primary">
             AutoTrade