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>

backend/app/api/themes.py

@@ -17,7 +17,7 @@ from fastapi import APIRouter, HTTPException, Query
 from sqlalchemy import text
 
 from app.db.connection import get_engine
-from app.seed.themes import THEMES, theme_by_slug, themes_index
+from app.seed.themes import THEMES, theme_by_slug, themes_for_code, themes_index
 
 router = APIRouter(prefix="/api/themes", tags=["themes"])
 
@@ -27,6 +27,112 @@ def list_themes() -> dict:
     return {"items": themes_index(), "total": len(THEMES)}
 
 
+@router.get("/peer/{code}")
+def peer_compare(
+    code: str,
+    window: int = Query(default=21, ge=2, le=252),
+    limit: int = Query(default=5, ge=1, le=20),
+) -> dict:
+    """동일 테마(들) 내 동종목 비교.
+
+    - 대상 종목이 속한 모든 테마의 코드 합집합 (자기 자신 제외) 을 peer 풀로 잡고,
+      각 종목의 최근 거래일 종가 / window 영업일 전 종가로 누적수익률을 구한다.
+    - peer 평균, 대상 종목 값, 상/하위 N 개 반환.
+    - 테마 무소속이면 themes=[] 빈 응답 (404 아님 — UI 가 그냥 패널을 숨기게).
+    """
+    themes = themes_for_code(code)
+    if not themes:
+        return {
+            "code": code,
+            "window": window,
+            "themes": [],
+            "self_pct": None,
+            "peer_avg_pct": None,
+            "top": [],
+            "bottom": [],
+        }
+
+    # 테마 합집합 코드 풀 (자기 자신 제외)
+    peer_codes: set[str] = set()
+    for t in themes:
+        peer_codes.update(t.codes)
+    peer_codes.discard(code)
+    pool = [code, *sorted(peer_codes)]
+
+    sql = text(
+        """
+        WITH ranked AS (
+          SELECT code, date, close,
+                 ROW_NUMBER() OVER (PARTITION BY code ORDER BY date DESC) AS rn
+            FROM ohlcv_daily
+           WHERE code = ANY(:codes) AND close IS NOT NULL
+        ),
+        latest AS (
+          SELECT code, close AS close_now, date AS date_now FROM ranked WHERE rn = 1
+        ),
+        base AS (
+          SELECT code, close AS close_base, date AS date_base FROM ranked WHERE rn = :w
+        )
+        SELECT s.code, s.name, s.market,
+               l.close_now, b.close_base,
+               CASE WHEN b.close_base > 0
+                    THEN (l.close_now - b.close_base) / b.close_base * 100
+                    ELSE NULL
+               END AS pct
+          FROM symbols s
+          LEFT JOIN latest l ON l.code = s.code
+          LEFT JOIN base   b ON b.code = s.code
+         WHERE s.code = ANY(:codes)
+        """
+    )
+
+    eng = get_engine()
+    with eng.connect() as conn:
+        rows = conn.execute(sql, {"codes": pool, "w": window}).all()
+
+    by_code: dict[str, dict] = {}
+    for r in rows:
+        by_code[r[0]] = {
+            "code": r[0],
+            "name": r[1],
+            "market": r[2],
+            "close": float(r[3]) if r[3] is not None else None,
+            "base_close": float(r[4]) if r[4] is not None else None,
+            "pct_change": float(r[5]) if r[5] is not None else None,
+        }
+
+    self_row = by_code.get(code)
+    self_pct = self_row["pct_change"] if self_row else None
+
+    peers = [
+        v for k, v in by_code.items() if k != code and v["pct_change"] is not None
+    ]
+    if peers:
+        peer_avg_pct = sum(p["pct_change"] for p in peers) / len(peers)
+        peers_sorted = sorted(peers, key=lambda x: x["pct_change"], reverse=True)
+        top = peers_sorted[:limit]
+        bottom = peers_sorted[-limit:][::-1]
+    else:
+        peer_avg_pct = None
+        top = []
+        bottom = []
+
+    return {
+        "code": code,
+        "name": self_row["name"] if self_row else code,
+        "window": window,
+        "themes": [
+            {"slug": t.slug, "name": t.name, "code_count": len(t.codes)}
+            for t in themes
+        ],
+        "self_pct": self_pct,
+        "peer_avg_pct": peer_avg_pct,
+        "peer_count": len(peers),
+        "top": top,
+        "bottom": bottom,
+    }
+
+
 @router.get("/{slug}")
 def get_theme(slug: str, limit: int = Query(default=30, ge=1, le=100)) -> dict:
     th = theme_by_slug(slug)

backend/app/seed/themes.py

@@ -229,3 +229,8 @@ def theme_by_slug(slug: str) -> Theme | None:
         if t.slug == slug:
             return t
     return None
+
+
+def themes_for_code(code: str) -> list[Theme]:
+    """주어진 종목 코드가 속한 테마들. 한 종목이 여러 테마에 동시 등재될 수 있음."""
+    return [t for t in THEMES if code in t.codes]