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>

trex_core/application/intents.py

@@ -163,16 +163,20 @@ class IntentService:
         elif not symbol:
             # No resolver wired and no symbol carried — cannot determine the order target.
             return IntentDecision(intent.intent_id, "rejected", None, "unknown_portfolio")
-        # Retry on the last-idle-slot race: another intent may claim the slot
+        # Retry on the last-candidate race: another intent may claim the slot
         # between our find and transit (SlotStateMismatchError).
+        # dcy-019 / REQ-007: admission candidate is idle ∪ closed (closed-slot
+        # reallocation), ordered by entry_count asc → updated_at asc → slot_id.
+        # The candidate may already be CLOSED, so the transit's from_state must
+        # follow the slot's current status rather than a hardcoded IDLE.
         for _ in range(_MAX_IDLE_RETRY):
-            slot = self._repo.find_idle_slot(intent.trading_date)
+            slot = self._repo.find_allocatable_slot(intent.trading_date)
             if slot is None:
                 return IntentDecision(intent.intent_id, "rejected", None, "no_idle_slot")
             try:
                 updated = self._svc.transit_slot(
                     slot.slot_id,
-                    SlotState.IDLE,
+                    slot.status,
                     SlotState.PENDING_BUY,
                     reason="buy_intent",
                     actor="intent_api",