feat(themes): 테마 인덱스/상세 (11 카테고리 · 111 종목)

- seed/themes.py: 반도체/2차전지/바이오/게임/엔터/자동차/금융/조선·방산/플랫폼·AI/유통·소비재/에너지 정적 매핑
- /api/themes (인덱스) + /api/themes/{slug} (종목 카드 + 최신 종가/등락)
- 홈에 ThemeTiles 그리드, /themes/{slug} 상세 페이지

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

backend/app/api/themes.py

@@ -0,0 +1,111 @@
+"""테마/카테고리 API.
+
+토스 '주식 골라보기' 의 테마 그리드와 비슷한 결.
+정적 매핑(seed/themes.py)을 베이스로, DB 에서 최신 종가/등락만 채워 응답.
+
+GET /api/themes
+  - 모든 테마 인덱스 (slug/name/description/code_count)
+
+GET /api/themes/{slug}
+  ?limit=20
+  - 해당 테마의 종목 카드 (종목명/시장/종가/등락률). 거래량 기준 정렬.
+  - ohlcv_daily 가 아직 안 채워져 있으면 close/pct_change 가 NULL.
+"""
+from __future__ import annotations
+
+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
+
+router = APIRouter(prefix="/api/themes", tags=["themes"])
+
+
+@router.get("")
+def list_themes() -> dict:
+    return {"items": themes_index(), "total": len(THEMES)}
+
+
+@router.get("/{slug}")
+def get_theme(slug: str, limit: int = Query(default=30, ge=1, le=100)) -> dict:
+    th = theme_by_slug(slug)
+    if th is None:
+        raise HTTPException(status_code=404, detail=f"unknown theme: {slug}")
+
+    codes = list(th.codes)[:limit]
+    if not codes:
+        return {
+            "slug": th.slug,
+            "name": th.name,
+            "description": th.description,
+            "items": [],
+        }
+
+    sql = text(
+        """
+        WITH last2 AS (
+          SELECT DISTINCT date FROM ohlcv_daily ORDER BY date DESC LIMIT 2
+        ),
+        bounds AS (SELECT MAX(date) AS d0, MIN(date) AS d1 FROM last2),
+        latest AS (
+          SELECT o.code, o.close AS close0, o.volume AS vol0
+            FROM ohlcv_daily o, bounds WHERE o.date = bounds.d0
+        ),
+        prev AS (
+          SELECT o.code, o.close AS close1
+            FROM ohlcv_daily o, bounds WHERE o.date = bounds.d1
+        )
+        SELECT s.code, s.name, s.market,
+               l.close0  AS close,
+               p.close1  AS prev_close,
+               l.vol0    AS volume,
+               CASE WHEN p.close1 > 0 THEN (l.close0 - p.close1) / p.close1 * 100 ELSE NULL END AS pct_change
+          FROM symbols s
+          LEFT JOIN latest l ON l.code = s.code
+          LEFT JOIN prev   p ON p.code = s.code
+         WHERE s.code = ANY(:codes)
+         ORDER BY vol0 DESC NULLS LAST, s.name ASC
+        """
+    )
+
+    eng = get_engine()
+    with eng.connect() as conn:
+        rows = conn.execute(sql, {"codes": codes}).all()
+
+    # symbols 테이블에 시드만 있고 codes 일부가 누락된 경우, 그래도 코드/이름 자리는 비워서 카드 표시.
+    by_code = {r[0]: r for r in rows}
+    items: list[dict] = []
+    for c in codes:
+        r = by_code.get(c)
+        if r is None:
+            items.append(
+                {
+                    "code": c,
+                    "name": c,  # symbols 미등재 — 코드로 노출
+                    "market": None,
+                    "close": None,
+                    "prev_close": None,
+                    "volume": None,
+                    "pct_change": None,
+                }
+            )
+        else:
+            items.append(
+                {
+                    "code": r[0],
+                    "name": r[1],
+                    "market": r[2],
+                    "close": float(r[3]) if r[3] is not None else None,
+                    "prev_close": float(r[4]) if r[4] is not None else None,
+                    "volume": int(r[5]) if r[5] is not None else None,
+                    "pct_change": float(r[6]) if r[6] is not None else None,
+                }
+            )
+
+    return {
+        "slug": th.slug,
+        "name": th.name,
+        "description": th.description,
+        "items": items,
+    }