feat(peers): 동종업종(테마) 비교 패널

- backend/app/seed/themes.py: themes_for_code(code) 헬퍼 추가 (코드 → 소속 테마들)
- backend/app/api/themes.py: GET /api/themes/peer/{code} 신규
  · 종목이 속한 모든 테마의 코드 합집합을 peer 풀로
  · 단일 SQL (ROW_NUMBER OVER PARTITION BY code) 로 21영업일 누적수익률 일괄 계산
  · 본인 / peer 평균 / 상·하위 5종목 반환
- web/lib/api.ts: PeerCompare 타입 + api.peerCompare()
- web/components/PeerComparePanel.tsx: 테마 태그 + 3-칸 요약 (본인/평균/격차) + 상·하위 5
- [code]/page.tsx 에 PeriodReturns 아래 부착. 테마 무소속 종목은 패널 자동 숨김.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

web/app/[code]/page.tsx

@@ -5,6 +5,7 @@ import { useEffect, useMemo, useState } from "react";
 import { CompositeScoreCard } from "../../components/CompositeScoreCard";
 import { DisclosuresPanel } from "../../components/DisclosuresPanel";
 import { MetricsPanel } from "../../components/MetricsPanel";
+import { PeerComparePanel } from "../../components/PeerComparePanel";
 import { NewsList } from "../../components/NewsList";
 import { PeriodReturns } from "../../components/PeriodReturns";
 import { PeriodTabs, periodSpec, type Period } from "../../components/PeriodTabs";
@@ -147,6 +148,9 @@ export default function CodePage({ params }: { params: { code: string } }) {
           <div className="mt-6">
             <PeriodReturns ohlcv={chart.ohlcv} />
           </div>
+          <div className="mt-6">
+            <PeerComparePanel code={code} />
+          </div>
           <div className="mt-6 grid gap-6 md:grid-cols-2">
             <TradingValuePanel data={chart.trading_value} />
             <MetricsPanel code={code} />