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>

tests/domain/slot/test_state.py

@@ -43,6 +43,8 @@ def test_advisory_lock_id_is_stable_constant():
         (SlotState.PENDING_SELL, SlotState.CLOSED),
         (SlotState.PENDING_SELL, SlotState.HOLDING),
         (SlotState.CLOSED, SlotState.IDLE),
+        # 9. closed-slot direct reallocation (dcy-019 / BAT-025)
+        (SlotState.CLOSED, SlotState.PENDING_BUY),
         # 8. * -> error
         (SlotState.IDLE, SlotState.ERROR),
         (SlotState.PENDING_BUY, SlotState.ERROR),
@@ -72,7 +74,6 @@ def test_allowed_transition(from_state: SlotState, to_state: SlotState):
         (SlotState.PENDING_SELL, SlotState.IDLE),
         (SlotState.PENDING_SELL, SlotState.PENDING_BUY),
         (SlotState.CLOSED, SlotState.HOLDING),
-        (SlotState.CLOSED, SlotState.PENDING_BUY),
         (SlotState.CLOSED, SlotState.PENDING_SELL),
         # error has restricted exits — only idle and holding allowed (REQ-004)
         (SlotState.ERROR, SlotState.PENDING_BUY),
@@ -92,5 +93,5 @@ def test_self_loops_are_not_allowed():
 
 
 def test_allowed_transitions_set_size():
-    """7 base + 5 to-error + 2 operator-resolve = 14 transitions."""
-    assert len(ALLOWED_TRANSITIONS) == 14
+    """8 base (incl. dcy-019 closed->pending_buy) + 5 to-error + 2 operator-resolve = 15."""
+    assert len(ALLOWED_TRANSITIONS) == 15