feat(messaging): 브로커 중립 메시징 플랫폼 24개 leaf 추가

messaging-superpowers-package 설계서/계획서 기반 구현.
registry를 19 → 43 leaf로 확장하고 src/messaging 아래 24개 leaf를 등록.

- core-api: M1 publish/consume + M2 batch·delayed·pause-resume
- policy/transport-spi: 재시도 결정, DLQ orchestration, admission control, lifecycle
- kafka·rabbit(Stable): contiguous commit, confirm/return 상관, 배치, 보안 설정
- pulsar·nats(Experimental): 기본 비활성, live 인증 없음을 코드로 기록
- outbox/inbox/claim-check: 트랜잭션 결합, lease, 무결성 검증
- admin: plan → approve → execute를 타입으로 강제
- 문서 9종, infra compose 7종, JMH 벤치마크 3종

검증: 아키텍처 게이트 3종 통과, 24개 leaf 전부 check 통과,
messaging 테스트 604개 통과/0 실패.

미완: 계획서가 요구한 실 브로커 IT 40개 중 7개만 작성.
Rabbit 13 / Outbox 6 / Inbox 4 / NATS·Pulsar·Share 5 / testkit 2 /
starter·admin 3, 그리고 TLS·ACL 2개가 남음.

infra/messaging/toxiproxy/docker-compose.yml

@@ -0,0 +1,19 @@
+# Toxiproxy, for the failures that matter most.
+#
+# The platform's hardest guarantee is that a lost confirmation is reported as AMBIGUOUS rather than
+# guessed. A healthy broker will not lose one on request, so the chaos suite puts a proxy in front of
+# it and severs the connection after the record was accepted but before the acknowledgement arrives.
+services:
+  toxiproxy:
+    image: ghcr.io/shopify/toxiproxy:2.12.0
+    container_name: messaging-toxiproxy
+    ports:
+      - "8474:8474"   # control API
+      - "19092:19092" # proxied Kafka
+      - "15673:15673" # proxied RabbitMQ
+      - "15433:15433" # proxied PostgreSQL
+    healthcheck:
+      test: ["CMD", "/toxiproxy-cli", "list"]
+      interval: 5s
+      timeout: 5s
+      retries: 20