docs(batch): draft-batch BAT-028 (dcy-020 BAT-β reconcile+admission) + design 확정

REQ-058(universe reconcile)+REQ-059(자산 admission FCFS/M)+REQ-060(max_active_slots).
design 확정(사용자 결정):
- D1: config 게이트 이중경로 (max_active_slots 설정 시 자산중심, 미설정 시 legacy pool;
  운영 데몬은 cutover 전까지 pool 무중단)
- D2: "활성"(M 캡) = holding+pending_buy+pending_sell
- D3: 대량소멸 가드 = N→0 + 급감(50%↓) 경고
batches/index BAT-028(standard, planning) 등록.

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

docs/batches/index.md

@@ -35,3 +35,4 @@
 | 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/) |
+| BAT-028 | standard | planning | REQ-058, REQ-059, REQ-060 | dcy-020 (BAT-β) | [bat-028](./bat-028_20260610_universe-reconcile-and-active-admission/) |