docs(batch): draft-batch BAT-027 (dcy-020 BAT-α 자산 영구 슬롯 토대) + design 확정(안 B)

REQ-056(영구 슬롯 스키마)+REQ-057(상태머신 재정의+인스턴스 lock) 토대 배치.
- planning: delivery plan/Design Gate(R-cascade)/milestones/risks
- design: R-cascade 실측(idle·closed/entry_count/전역 lock/trading_date 소비처) +
  접근안 A/B/C → 안 B(점진/additive-first) 확정:
  * additive 스키마(instance_key·retired_at, entry_count/trading_date 유지→BAT-δ drop)
  * inactive 표준 + idle/closed 별칭(closed→idle 제거)
  * advisory lock 인스턴스 스코프화
  * 부분 UNIQUE(instance_key, portfolio_id) WHERE portfolio_id NOT NULL
  * instance_key NOT NULL DEFAULT 'default'
- batches/index BAT-027(standard, planning) 등록

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

docs/batches/index.md

@@ -34,3 +34,4 @@
 | BAT-024 | batch-lite | release-candidate | REQ-032 (CHG-20260609-01) | dcy-016 (issue #17) | [bat-024](./bat-024_20260609_operator-enter-forced-close-at/) |
 | BAT-025 | standard | release-candidate | REQ-002 (CHG-20260609-01), REQ-003 (CHG-20260609-01), REQ-006 (CHG-20260609-01), REQ-007 (CHG-20260609-01), REQ-009 (CHG-20260609-01) | dcy-019 (issue #18) | [bat-025](./bat-025_20260609_slot-entry-count-and-closed-reallocation/) |
 | BAT-026 | batch-lite | release-candidate | REQ-048 (CHG-20260609-01), REQ-010 (CHG-20260609-01) | 없음 (trex-orb-v1 정합) | [bat-026](./bat-026_20260609_config-dir-env-and-config-path/) |
+| BAT-027 | standard | planning | REQ-056, REQ-057 | dcy-020 (BAT-α) | [bat-027](./bat-027_20260610_asset-permanent-slot-foundation/) |