feat(pnl): trade history + realized PnL API (WAC) — BAT-017, REQ-039~042 Implemented

- GET /v1/portfolios/{id}/trades and GET /v1/portfolios/{id}/pnl/realized endpoints
- Weighted Average Cost (WAC) realized PnL calculation in app/domain/pnl.py
- cost_basis and data_completeness_warning returned in pnl API response
- Test coverage: 50 passed (WAC 20 + trades 12 + pnl 18), full 427 passed regression ✓
- WAC validated against 199,300 unit e2e test cases
- DB migration: none required
- QC: qc-reviewer PASS-WITH-NOTES; team lead confirm-batch-verification → release-candidate
- Remaining non-blocking: symbol filter edge case testing, HTTP_422 deprecation

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01VHtM5Ws1HKCKQ4JGi6GRb5

docs/srs/Integration/req-041_wac-cost-basis-pnl-calculation.md

@@ -1,6 +1,6 @@
 # REQ-041: WAC 기반 cost_basis 산출 및 실현 PnL 계산 로직 (service/domain 계층 격리)
 
-- Status: Approved
+- Status: Implemented
 - Type: Integration
 - Priority: High
 - Owner: Justin Ko
@@ -87,3 +87,10 @@
 
 #### Change Summary
 - confirm-req: `Proposed` → `Approved`. WAC 공식 확정(FIFO 제외), NFR-3 격리 AC-7/AC-8·R-1 완화 AC-3/AC-4 확인, blocker 없음. 구현 위치(domain vs service)는 구현 단계 결정. M1 fast-track.
+
+### CHG-20260618-03
+- Date: 2026-06-18
+- Author: 팀장 (Claude)
+
+#### Change Summary
+- confirm-req-implemented: `Approved` → `Implemented`. Evidence: app/domain/pnl.py 구현, WAC 누적 정확성+199,300 검증, NFR-3 격리(psycopg import 0) QC 확인, R-1 경고 동작, test_wac_calculation.py 20 passed.