feat(bat-053): 그날-시작 KIS 인증정보 fetch + fail-safe 로드 (REQ-112~115)

REQ-112: BrokerCredentialPayload/TradingContext 데이터클래스 + PortfolioHubReadPort.fetch_broker_credential() 포트 메서드 + hub_read 어댑터(_fetch_user_info 헬퍼 추출) + stub_read 결정론 stub
REQ-113: DaemonInstanceConfig/DaemonConfig.credential_fetch_enabled opt-in(기본 False) + TOML 파싱 + break-glass(TREX_KIS_BROKER_BREAK_GLASS) 감지
REQ-114: SnapshotScheduler._maybe_fetch_credential() — fail-closed 3조건(unavailable/broker-null/trading_disabled) + CRITICAL 알람 DAY_START_LOAD_FAILED + IntentService entry_allowed_fn 게이트(BuyIntent 차단, SellIntent 통과)
REQ-115: 그날 고정 캐시(_cached_credential/_credential_date) — 동일 날짜 재fetch 방지 + app_secret 메모리 한정(Redis 미기록)

스텁 기반 구현: 실 portfolio-hub/네트워크 없이 AC 전부 단위 테스트.
회귀: credential_fetch_enabled=False(기본) 경로 byte-for-byte 보존.
745 passed, 47 skipped (0 failed).

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01VHtM5Ws1HKCKQ4JGi6GRb5

docs/batches/index.md

@@ -60,3 +60,4 @@
 | BAT-050 | standard | release-candidate | REQ-102, REQ-103, REQ-104, REQ-107, REQ-108 | dcy-034 (core-A) | [bat-050](./bat-050_20260626_reconcile-warning-blocking-gate-core-a/) |
 | BAT-051 | standard | release-candidate | REQ-105, REQ-106 | dcy-034 (core-B) | [bat-051](./bat-051_20260626_sync-verify-cli-cold-start-core-b/) |
 | BAT-052 | standard | release-candidate | REQ-109, REQ-110, REQ-111 | dcy-035 | [bat-052](./bat-052_20260626_wac-realized-pnl-report/) |
+| BAT-053 | standard | in-progress | REQ-112, REQ-113, REQ-114, REQ-115 | dcy-036 | [bat-053](./bat-053_20260628_daystart-credential-fetch-failsafe/) |