feat(slot,intent): slot strategy-state 저장소 (dcy-028) + sell retryable 플래그 (issue #27)

BAT-042 (dcy-028 / issue #26 C-1/C-2/C-2b/C-3, REQ-079~082 + REQ-073/074 CHG):
- slot_strategy_state 별도 테이블 + StrategyStateStore(in-memory+PG) + occupancy_seq·version CAS + opaque UTF-8 data + 2단 size cap (REQ-079)
- trex.slots.strategy_state.set write RPC — reject reason 집합, 멱등 (REQ-080)
- Slot.occupancy_seq 필드 + inactive→pending_buy bump + →INACTIVE close 삭제 훅 → 점유 전환 ABA 구조적 차단 (REQ-081)
- slots.req 응답 행에 strategy_state 맵(batched 조립)·occupancy_seq additive (REQ-073 AC-7/REQ-074 AC-6)
- 마이그레이션 014(occupancy_seq)/015(slot_strategy_state), baseline 문서 정합 (REQ-082)

BAT-043 (issue #27 / REQ-007 CHG):
- rejected SellIntent 응답에 additive retryable: bool (core 소유 reason→retryable 매핑, 미인식 기본 true, bad_request* false) — 손절매 재시도 안전 경로 decoupling

검증: 487 passed, 47 skipped (신규 41: store CAS 6+ABA, occupancy bump/close 4경로, set RPC 9, slots read 5, retryable 8, PG 게이트), ruff clean.
REQ-079·080·081·082·073·074·007 → Implemented. issue #27 close. PG 경로 실 DB 검증은 release 위임.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

trex_core/application/portfolio.py

@@ -272,6 +272,9 @@ def slot_to_dict(
         "portfolio_id": s.portfolio_id,
         "forced_close_at": s.forced_close_at.isoformat() if s.forced_close_at else None,
         "universe_detached": getattr(s, "retired_at", None) is not None,
+        # dcy-028/REQ-081 (BAT-042): per-occupancy guard counter — the strategy
+        # daemon echoes this as expected_occupancy_seq on strategy_state writes.
+        "occupancy_seq": getattr(s, "occupancy_seq", 0),
     }
 
     # hub authority: asset_quantity (hub primary) + cash_balance