feat: 한국 현황 상단에 중국어선감시 버튼 추가

frontend/src/App.tsx

@@ -307,6 +307,15 @@ function AuthenticatedApp({ user, onLogout }: AuthenticatedAppProps) {
               <span className="text-[11px]">🚢</span>
               {t('filters.ferryWatch')}
             </button>
+            <button
+              type="button"
+              className={`mode-btn ${koreaLayers.cnFishing ? 'active live' : ''}`}
+              onClick={() => toggleKoreaLayer('cnFishing')}
+              title="중국어선감시"
+            >
+              <span className="text-[11px]">🎣</span>
+              중국어선감시
+            </button>
           </div>
         )}