feat(slot): slot entry_count + closed-slot reallocation (dcy-019, BAT-025) + REL-005

dcy-019/issue #18: slot 자원을 진입 횟수 기준으로 고르게 재사용하고 idle 소진 시
closed 슬롯을 직접 재할당한다. 거버넌스는 전부 change-req(신규 REQ 없음).

- 도메인(REQ-002): Slot.entry_count(기본 0) + EXPECTED_SLOT_FIELDS, 상태 머신
  closed→pending_buy 신규 전이(base 8→9, ALLOWED_TRANSITIONS 14→15),
  _apply_transition_fields closed→pending_buy clean-slate + →pending_buy 시 +1
- 영속화(REQ-006): 멱등 마이그레이션 008(entry_count), flat 매핑,
  find_allocatable_slot(idle∪closed, entry_count→updated_at→slot_id) + in-memory 동등
- admission(REQ-007): _admit_buy find_idle_slot→find_allocatable_slot + from_state=slot.status
- 테스트(REQ-003): 전이 카운트/계약 가드 정합 + test_slot_entry_count.py / test_buy_admission_reallocation.py
- 문서(REQ-009): data-model.md / runtime-flows.md 정합
- 기존 daily_symbol_entries(symbol-scoped) 분리·미변경

BAT-025(release-candidate) delivery + change-req REQ-002/003/006/007/009(CHG-20260609-01).
REL-005(confirmed, app-service): BAT-024+BAT-025 묶음. operator-facing run-the-app
스모크로 enter --forced-close-at(BAT-024)·closed 재할당(BAT-025) 실 데몬 검증
(실 PG 마이그레이션 008 round-trip 포함).

검증: 단위 366 passed / 35 skipped(KIS sandbox 1건 deselect — live .env 환경 의존), ruff clean.

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

docs/releases/index.md

@@ -12,3 +12,4 @@
 | REL-002 | tooling | feedback-captured | BAT-009 | Change-req: paper execution_id Redis(#4) | [rel-002](rel-002_20260606_paper-broker-env-tuning.md) |
 | REL-003 | app-service | feedback-captured | BAT-010, BAT-011, BAT-012, BAT-013 | dcy-007 (자율 안전 매도) + dcy-008 (kill-switch) + dcy-009 (다중 인스턴스 토폴로지) — 통합 릴리즈 | [rel-003](rel-003_20260607_safety-killswitch-multi-instance.md) |
 | REL-004 | app-service | feedback-captured | BAT-014, BAT-015, BAT-016, BAT-017, BAT-018, BAT-019, BAT-020, BAT-021, BAT-022, BAT-023 | dcy-010 (safety-sell 쿨다운) + dcy-011~017 (buy/sell 계약·KIS 취소·trading_date TZ·ledger 백오프 버그픽스 + 운영자 CLI + 워치독 가시화) + dcy-016 후속(슬롯 상태 가시화) + dcy-018 (ledger 현금/포지션 write-back, option D) — 통합 릴리즈 | [rel-004](rel-004_20260608_safety-cooldown-bugfix-hardening-cli.md) |
+| REL-005 | app-service | confirmed | BAT-024, BAT-025 | dcy-016 후속/issue #17 (operator enter --forced-close-at) + dcy-019/issue #18 (slot entry_count + closed 슬롯 재할당) — 통합 릴리즈 | [rel-005](rel-005_20260609_operator-forced-close-and-slot-reallocation.md) |