feat(stock-lab): 포트폴리오 매입가(purchase_price) 컬럼 분리 + 원달러 환율 부호 보정

원달러 환율:
- 네이버 환율 change_value에 부호가 없어 프론트에서 항상 상승으로 인식되던 문제
- direction(red/blue) 기반으로 +/- 부호 prepend

포트폴리오:
- portfolio 테이블에 purchase_price 컬럼 추가 (기존 row는 avg_price로 백필)
- avg_price(평균단가): 손익률 계산 기준 (cost_basis)
- purchase_price(매입가): 총 매입 금액 요약 표시 기준
- API: PortfolioItemRequest/UpdateRequest에 purchase_price(Optional) 추가
- GET /api/portfolio 응답 holdings에 purchase_price 포함, summary.total_buy는 매입가 합계, total_profit_rate는 평균단가 기준

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

stock-lab/app/main.py

@@ -284,7 +284,8 @@ class PortfolioItemRequest(BaseModel):
     ticker: str
     name: str
     quantity: int
-    avg_price: int
+    avg_price: int                          # 평균단가 (현재가 평가/손익 계산용)
+    purchase_price: Optional[int] = None    # 매입가 (총 매입 금액 계산용, 미입력 시 avg_price로 자동 설정)
 
 
 class PortfolioUpdateRequest(BaseModel):
@@ -293,6 +294,7 @@ class PortfolioUpdateRequest(BaseModel):
     name: Optional[str] = None
     quantity: Optional[int] = None
     avg_price: Optional[int] = None
+    purchase_price: Optional[int] = None
 
 
 @app.get("/api/portfolio")
@@ -320,15 +322,20 @@ def get_portfolio():
     prices = get_current_prices(tickers)
 
     holdings = []
-    total_buy = 0
+    total_buy = 0           # 요약 표시용 (purchase_price 기반)
+    total_cost_basis = 0    # 손익률 계산용 (avg_price 기반)
     total_eval = 0
 
     for item in items:
         current_price = prices.get(item["ticker"])
-        buy_amount = item["avg_price"] * item["quantity"]
+        # avg_price: 평균단가 — 손익(평가금액 - 매입원가) 계산 기준
+        # purchase_price: 매입가 — 총 매입 금액 표시 기준 (없으면 avg_price로 폴백)
+        purchase_price = item.get("purchase_price") if item.get("purchase_price") is not None else item["avg_price"]
+        cost_basis = item["avg_price"] * item["quantity"]
+        buy_amount = purchase_price * item["quantity"]
         eval_amount = current_price * item["quantity"] if current_price is not None else None
-        profit_amount = (eval_amount - buy_amount) if eval_amount is not None else None
-        profit_rate = round((profit_amount / buy_amount) * 100, 2) if (profit_amount is not None and buy_amount) else None
+        profit_amount = (eval_amount - cost_basis) if eval_amount is not None else None
+        profit_rate = round((profit_amount / cost_basis) * 100, 2) if (profit_amount is not None and cost_basis) else None
 
         holdings.append({
             "id": item["id"],
@@ -337,6 +344,7 @@ def get_portfolio():
             "name": item["name"],
             "quantity": item["quantity"],
             "avg_price": item["avg_price"],
+            "purchase_price": purchase_price,
             "current_price": current_price,
             "eval_amount": eval_amount,
             "profit_amount": profit_amount,
@@ -344,11 +352,13 @@ def get_portfolio():
         })
 
         total_buy += buy_amount
+        total_cost_basis += cost_basis
         if eval_amount is not None:
             total_eval += eval_amount
 
-    total_profit = total_eval - total_buy
-    total_profit_rate = round((total_profit / total_buy) * 100, 2) if total_buy else 0.0
+    # 손익은 실제 평균단가(cost_basis) 기준으로 계산
+    total_profit = total_eval - total_cost_basis
+    total_profit_rate = round((total_profit / total_cost_basis) * 100, 2) if total_cost_basis else 0.0
 
     return {
         "holdings": holdings,
@@ -367,7 +377,10 @@ def get_portfolio():
 @app.post("/api/portfolio", status_code=201)
 def create_portfolio_item(req: PortfolioItemRequest):
     """포트폴리오 종목 추가"""
-    item_id = add_portfolio_item(req.broker, req.ticker, req.name, req.quantity, req.avg_price)
+    item_id = add_portfolio_item(
+        req.broker, req.ticker, req.name, req.quantity, req.avg_price,
+        purchase_price=req.purchase_price,
+    )
     return {"id": item_id, "ok": True}