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/Testing/req-042_trade-pnl-api-test-coverage.md

@@ -1,6 +1,6 @@
 # REQ-042: 체결 내역/실현 PnL API 테스트 커버리지 (WAC 시나리오 기댓값 대조, 날짜 필터, 422)
 
-- Status: Approved
+- Status: Implemented
 - Type: Testing
 - Priority: High
 - Owner: Justin Ko
@@ -98,3 +98,10 @@
 
 #### Change Summary
 - confirm-req: `Proposed` → `Approved`. WAC 시나리오 기댓값·날짜필터·422·R-1 경고 검증 AC가 REQ-039~041과 정합, blocker 없음. 구현 REQ와 동일 batch. M1 fast-track.
+
+### CHG-20260618-03
+- Date: 2026-06-18
+- Author: 팀장 (Claude)
+
+#### Change Summary
+- confirm-req-implemented: `Approved` → `Implemented`. Evidence: 3개 테스트 파일 50 passed(20+12+18) 독립 QC 재현, 전체 427 passed 회귀 없음. AC-1~6 충족.