feat(agent): service systemd DynamicUser + documentation déploiement

- Ajoute deploy/nanometrics-agent.service avec DynamicUser, ProtectSystem,
  PrivateTmp, NoNewPrivileges et RestrictAddressFamilies
- Ajoute deploy/README.md avec procédure d'installation/désinstallation
- Corrige 3 avertissements clippy : iter_kv_map (network.rs) et
  collapsible_match (mqtt.rs)

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

deploy/README.md

@@ -0,0 +1,43 @@
+# Déploiement de l'agent Nanometrics
+
+## Prérequis
+
+- Debian/Ubuntu amd64
+- systemd
+
+## Installation
+
+```bash
+# Copier le binaire
+sudo cp ../agent/target/release/nanometrics-agent /usr/local/bin/
+sudo chmod 755 /usr/local/bin/nanometrics-agent
+
+# Créer la configuration
+sudo mkdir -p /etc/nanometrics
+sudo cp ../agent/config.toml.example /etc/nanometrics/config.toml
+sudo nano /etc/nanometrics/config.toml  # ajuster server.ip
+
+# Installer et démarrer le service
+sudo cp nanometrics-agent.service /etc/systemd/system/
+sudo systemctl daemon-reload
+sudo systemctl enable nanometrics-agent
+sudo systemctl start nanometrics-agent
+sudo systemctl status nanometrics-agent
+```
+
+## Vérification
+
+```bash
+sudo journalctl -u nanometrics-agent -f
+```
+
+## Désinstallation
+
+```bash
+sudo systemctl stop nanometrics-agent
+sudo systemctl disable nanometrics-agent
+sudo rm /etc/systemd/system/nanometrics-agent.service
+sudo rm /usr/local/bin/nanometrics-agent
+sudo rm -rf /etc/nanometrics
+sudo systemctl daemon-reload
+```

deploy/nanometrics-agent.service

@@ -0,0 +1,24 @@
+[Unit]
+Description=Nanometrics Agent — collecte de métriques système
+After=network.target
+Documentation=https://git.maison43gil.com/gilles/nano_metrics
+
+[Service]
+Type=simple
+ExecStart=/usr/local/bin/nanometrics-agent /etc/nanometrics/config.toml
+Restart=on-failure
+RestartSec=5
+
+DynamicUser=yes
+ConfigurationDirectory=nanometrics
+ConfigurationDirectoryMode=0750
+
+ProtectSystem=strict
+ProtectHome=read-only
+PrivateTmp=yes
+NoNewPrivileges=yes
+
+RestrictAddressFamilies=AF_INET AF_INET6 AF_UNIX
+
+[Install]
+WantedBy=multi-user.target