feat(stock): 포트폴리오 현재가에 NXT 시간외 거래 뱃지

백엔드 응답의 price_session에 따라 NXT 프리마켓/애프터마켓 거래 중인
종목에 작은 'NXT' / 'NXT 프리' 뱃지를 표시. 툴팁에 거래 시각 노출.
정규장 마감 후에도 평가금액이 자연스럽게 이어지는 흐름을 시각적으로 보강.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/pages/stock/Stock.css

@@ -901,6 +901,22 @@
     font-style: italic;
 }
 
+.pf-nxt-badge {
+    display: inline-block;
+    margin-left: 6px;
+    padding: 1px 6px;
+    border-radius: 4px;
+    border: 1px solid rgba(139, 92, 246, 0.45);
+    background: rgba(139, 92, 246, 0.12);
+    color: #c4b5fd;
+    font-size: 10px;
+    font-weight: 600;
+    letter-spacing: 0.04em;
+    vertical-align: middle;
+    cursor: help;
+    white-space: nowrap;
+}
+
 .pf-edit-row {
     grid-column: 1 / -1;
     display: grid;

src/pages/stock/components/PortfolioTab.jsx

@@ -6,6 +6,26 @@ import {
 } from 'recharts';
 import { formatNumber, formatPercent, toNumeric, profitColorClass, numFitClass } from '../stockUtils';
 
+const formatPriceTime = (iso) => {
+    if (!iso) return '';
+    const d = new Date(iso);
+    if (Number.isNaN(d.getTime())) return '';
+    return `${String(d.getHours()).padStart(2, '0')}:${String(d.getMinutes()).padStart(2, '0')}`;
+};
+
+const PriceSessionBadge = ({ session, asOf }) => {
+    if (session !== 'NXT_AFTER' && session !== 'NXT_PRE') return null;
+    const isPre = session === 'NXT_PRE';
+    const label = isPre ? 'NXT 프리' : 'NXT';
+    const desc = isPre ? 'NXT 프리마켓 거래가' : 'NXT 야간거래 (15:30~20:00)';
+    const time = formatPriceTime(asOf);
+    return (
+        <span className="pf-nxt-badge" title={time ? `${desc} · ${time}` : desc}>
+            {label}
+        </span>
+    );
+};
+
 const PortfolioTab = ({ pf, asset, handleSell, handleSaveSnapshot }) => (
     <>
         {pf.portfolioError ? (
@@ -527,6 +547,10 @@ const PortfolioTab = ({ pf, asset, handleSell, handleSaveSnapshot }) => (
                                                     {item.current_price != null
                                                         ? formatNumber(item.current_price)
                                                         : '조회 실패'}
+                                                    <PriceSessionBadge
+                                                        session={item.price_session}
+                                                        asOf={item.price_as_of}
+                                                    />
                                                 </strong>
                                             </div>
                                             <div className="stock-holdings__metric">