feat(markets): /api/markets/movers + /related/{code} + 홈/종목 페이지 연동

backend:
  - 신규 라우터 app/api/markets.py
  - GET /api/markets/movers?market=ALL|KOSPI|KOSDAQ&limit=10
    → gainers / losers / by_volume 3 카테고리. ohlcv_daily 최신 2 거래일 비교.
  - GET /api/markets/related/{code}?limit=8
    → 같은 market 내 거래량 상위 (sector 컬럼은 시드 단계 NULL 다수라 제외).
  - main.py 에 라우터 include.

frontend:
  - lib/api.ts 에 Mover/MoversResponse/RelatedResponse 타입 + .movers/.related 추가.
  - components/MarketsOverview.tsx: 등락 상위 / 등락 하위 / 거래량 상위 3 컬럼.
  - components/RelatedStocks.tsx: 같은 시장 내 관련 종목 8 개.
  - 홈 페이지에 MarketsOverview 배치 (SeedTiles 아래).
  - 종목 페이지 우측 사이드바 컬럼에 RelatedStocks 추가 (SymbolSidebar 아래).

verify: py_compile clean, tsc --noEmit clean, next lint clean.

backend/app/main.py

@@ -9,6 +9,7 @@ from fastapi.middleware.cors import CORSMiddleware
 from sqlalchemy import text
 
 from app.api.chart import router as chart_router
+from app.api.markets import router as markets_router
 from app.api.metrics import router as metrics_router
 from app.api.news import router as news_router
 from app.api.predict import router as predict_router
@@ -102,6 +103,7 @@ app.include_router(chart_router)
 app.include_router(predict_router)
 app.include_router(metrics_router)
 app.include_router(news_router)
+app.include_router(markets_router)
 
 
 def _resolved_device() -> str: