feat(safety-sell): dcy-017 워치독 소유권 가시화 — snapshot 상태 + 발동 로깅 (BAT-021)

전략 이탈로 슬롯이 내부 청산 루틴(워치독) 소유로 넘어간 상태가 무성이라
운영자가 인지할 수 없던 문제(issue #12)를 가시화한다.

거버넌스: 전부 change-req (신규 REQ 없음, dcy-017 OQ-3; Redis 미채택).
- REQ-034/021: WatchdogStore.last_seen + snapshot RPC 응답에 holding 슬롯
  워치독 상태(expired/last_seen) read-only 동봉(best-effort)
- REQ-032: trex-core slots 가 expired 슬롯을 WATCHDOG-OWNED(전략 이탈) 표시
- REQ-037/038/039: safety-sell 워치독 소유 진입(WARN)/이탈(INFO) + 발동
  (forced_close·stop_loss=WARN, take_profit·market_close=INFO) 로그 +
  in-process 카운터(SafetySellService.counters), 구조화 필드(slot_id/
  portfolio_id/reason/phase/instance_key). per-tick 스킵은 카운터만
- REQ-042: runtime-flows/interface-contract 정합

best-effort 격리(NFR-1): 모든 가시화는 예외 격리 — 워치독 판정·청산 불변.
dcy-016 억제 읽기로 관측이 워치독을 리셋하지 않음(비침습).

검증: 단위 335 passed/34 skipped, 인프라 게이트(PG+RabbitMQ) 369 passed, ruff clean.
신규 test_safety_sell_visibility(6) + snapshot watchdog(1) + CLI(1). BAT-021 rc.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

docs/batches/index.md

@@ -28,3 +28,4 @@
 | BAT-018 | standard | release-candidate | REQ-005 (CHG-20260608-01), REQ-048 (CHG-20260608-01), REQ-009 (CHG-20260608-01) | dcy-014 | [bat-018](./bat-018_20260608_trading-date-timezone-daily-preallocation/) |
 | BAT-019 | standard | release-candidate | REQ-017 (CHG-20260608-01), REQ-019 (CHG-20260608-01), REQ-018 (CHG-20260608-03), REQ-020 (CHG-20260608-01) | dcy-015 | [bat-019](./bat-019_20260608_ledger-outbox-permanent-error-backoff/) |
 | BAT-020 | standard | release-candidate | REQ-032 (CHG-20260608-01), REQ-022 (CHG-20260608-01), REQ-021 (CHG-20260608-02), REQ-034 (CHG-20260608-01), REQ-026 (CHG-20260608-01) | dcy-016 | [bat-020](./bat-020_20260608_operator-cli-rpc-commands/) |
+| BAT-021 | standard | release-candidate | REQ-034 (CHG-20260608-02), REQ-021 (CHG-20260608-03), REQ-037 (CHG-20260608-01), REQ-038 (CHG-20260608-01), REQ-039 (CHG-20260608-01), REQ-032 (CHG-20260608-02), REQ-042 (CHG-20260608-01) | dcy-017 | [bat-021](./bat-021_20260608_watchdog-ownership-visibility/) |