style: 카테고리 영문 헤딩 42px 볼드, INFINITH 퍼플(#6C5CE7), Playfair 적용

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

src/pages/DiscoveryReportPage.tsx

@@ -191,7 +191,7 @@ export default function DiscoveryReportPage() {
                       <Icon size={22} />
                     </div>
                     <div>
-                      <p className="text-sm font-semibold text-slate-400 tracking-wide">
+                      <p className="font-serif text-4xl md:text-[42px] font-bold text-[#6C5CE7] tracking-[-0.01em] leading-tight">
                         {cs.category.code} · {cs.category.nameEn}
                       </p>
                       <h3 className="text-xl font-bold">{cs.category.name}</h3>