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/domain/slot/service.py

@@ -201,6 +201,19 @@ class SlotService:
                 updated_at=datetime.now(tz=timezone.utc),
             )
 
+        # dcy-019 / REQ-002 (BAT-025): closed-slot direct reallocation. A closed
+        # slot still carries the prior cycle's occupancy; start from a clean
+        # slate so a previous position/broker handle never leaks into the new
+        # entry. entry_count is intentionally preserved (slot-scoped cumulative).
+        if to_state is SlotState.PENDING_BUY and slot.status is SlotState.CLOSED:
+            slot = replace(
+                slot,
+                symbol=None, qty=None, avg_price=None, limit_price=None,
+                allocated_capital=None, order_id=None, strategy_id=None,
+                broker_order_id=None, portfolio_id=None, sell_strategy_id=None,
+                forced_close_at=None, stop_loss_price=None, take_profit_price=None,
+            )
+
         # limit_price lifecycle (dcy-012 FR-1): set only on entering a pending
         # state (the order's limit); cleared on entering HOLDING/CLOSED.
         if to_state in {SlotState.PENDING_BUY, SlotState.PENDING_SELL}:
@@ -208,6 +221,10 @@ class SlotService:
         else:  # HOLDING / CLOSED — pending order limit no longer applies.
             new_limit_price = None
 
+        # dcy-019 / REQ-002: +1 on each allocation transition (→pending_buy),
+        # for both idle→pending_buy and closed→pending_buy (FR-4).
+        new_entry_count = slot.entry_count + (1 if to_state is SlotState.PENDING_BUY else 0)
+
         # Generic update: caller-supplied fields override; None means "keep".
         return replace(
             slot,
@@ -241,6 +258,7 @@ class SlotService:
             take_profit_price=(
                 take_profit_price if take_profit_price is not None else slot.take_profit_price
             ),
+            entry_count=new_entry_count,  # dcy-019 / REQ-002
             updated_at=datetime.now(tz=timezone.utc),
         )