feat(agent-scan-network): MQTT + configs exemples + ROADMAP Phase 6

- mqtt.rs : publication résumé scan sur sentinelmesh/<host>/network/scan
- Config MQTT dans les deux agents (enabled: false par défaut)
- ROADMAP Phase 6 complète : SSE, historique, Prometheus, MQTT ✅

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

agents/agent-scan-network/Cargo.toml

@@ -16,3 +16,4 @@ reqwest          = { version = "0.12", features = ["json"] }
 chrono           = { version = "0.4", features = ["serde"] }
 ipnetwork        = "0.20"
 tokio-util       = "0.7"
+rumqttc          = "0.24"