chore(0004): close issue, bump unibus to 0.5.0, record dataplane-acl decision

Issue 0004 (security hardening) done across 0004a-0004f. app.md version 0.5.0
with the capability growth log entry; dev/0004d-dataplane-acl.md documents the
chosen minimum-defense strategy for the NATS data plane and its residual limit
(per-subject ACL deferred to 0003). Full work report in
projects/message_bus/reports/0005-2026-06-07-unibus-security-hardening.md.

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

dev/issues/0004-security-hardening.md

@@ -1,8 +1,10 @@
 ---
 issue: 0004
 title: Hardening de seguridad — autorización, anti-DoS y confidencialidad antes de exponer público
-status: spec
+status: done
 created: 2026-06-07
+completed: 2026-06-07
+report: projects/message_bus/reports/0005-2026-06-07-unibus-security-hardening.md
 domain: security
 scope: unibus (pkg/membership/server.go, auth.go, pkg/embeddednats, pkg/client, cmd/membershipd, deploy/tls)
 depends_on: 0001 (cierra los gaps que la auditoría 0004 encontró sobre lo entregado en 0001)