chore(0006): bump unibus to 0.8.0, close issue 0006 (cluster hardening + wiring)

All seven phases (0006a–0006g) merged: blockers N3 (replicated nonce) and N2
($JS.API.> KV leak) closed, decentralized KV store wired (--store kv), homogeneous
cluster posture enforced (N1), RefreshSession in all clients (N4), the lows
(secret out of argv, migrate guard, R1/CA docs), and the 3-node deploy material.

Full suite + every audit-0008 attack regression green; govulncheck 0 reachable.
See report 0009.

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

dev/issues/0006-cluster-hardening-and-wiring.md

@@ -1,8 +1,10 @@
 ---
 issue: 0006
 title: Completar y endurecer el cluster — wiring del control plane KV + N1-N6 de la auditoría 0008
-status: spec
+status: done
 created: 2026-06-07
+closed: 2026-06-07
+closed_by: fases 0006a–0006g (ver report 0009); unibus v0.8.0
 domain: security
 scope: unibus (cmd/membershipd, pkg/membership, pkg/embeddednats, pkg/busauth, pkg/client)
 depends_on: 0003 (completa su wiring), 0005 (hereda el bus single-node ya seguro)