feat(symbol-page): intraday short-term returns + hline storage-failure guard

- IntradayReturns: 10분/30분/1시간/3시간/시가대비 mini cards for 1D mode
  (PeriodReturns labels lie when interval is 10m; swap them out by isIntraday)
- addLine/removeLine/clearLines now return previous state when localStorage
  write fails — UI no longer diverges from storage in locked-storage env

addresses reviewer 318eae6 non-blocking caveat about write-failure divergence

web/app/[code]/page.tsx

@@ -5,6 +5,7 @@ import { useEffect, useMemo, useState } from "react";
 import { AlertsPanel } from "../../components/AlertsPanel";
 import { CompositeScoreCard } from "../../components/CompositeScoreCard";
 import { DisclosuresPanel } from "../../components/DisclosuresPanel";
+import { IntradayReturns } from "../../components/IntradayReturns";
 import { InvestmentNote } from "../../components/InvestmentNote";
 import { InvestorCumulative } from "../../components/InvestorCumulative";
 import { MetricsPanel } from "../../components/MetricsPanel";
@@ -246,7 +247,12 @@ export default function CodePage({ params }: { params: { code: string } }) {
             <CompositeScoreCard chart={chart} />
           </div>
           <div className="mt-6">
-            <PeriodReturns ohlcv={chart.ohlcv} />
+            {/* 1D(10분봉) 모드에선 PeriodReturns 의 거래일 라벨이 거짓이 되므로 단기 카드로 교체 */}
+            {isIntraday ? (
+              <IntradayReturns ohlcv={chart.ohlcv} />
+            ) : (
+              <PeriodReturns ohlcv={chart.ohlcv} />
+            )}
           </div>
           <div className="mt-6">
             <PeerComparePanel code={code} />