feat(monitoring): surveillance réseau active via blackbox_exporter

Sondes actives ICMP/HTTP/DNS qui complètent le monitoring passif
(node_exporter + up{}) : joignabilité hôtes/passerelle, accès internet,
santé DNS *.lab.local + forwarding, latence LAN, services de bout en
bout via Traefik.

- blackbox_exporter (chart 11.13.0, ArgoCD, ns monitoring) — ICMP via
  NET_RAW, DNS du pod = dnsmasq (chemin réel lab → Traefik)
- 3 jobs blackbox-icmp/-http/-dns (additionalScrapeConfigs)
- alerts-network.yaml : internet, DNS, passerelle, hôtes, services,
  latence, exporter (→ pipeline AlertManager existant)
- Asa : outil network_status + contexte présélectionnable reseau
- doc admin/infra/reseau.md + CLAUDE.md + progress

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Rc3dLKfqEPHexvFCCx5ZEF

stt/server/stt_server/sources.py

@@ -263,12 +263,43 @@ async def metrics_block(client: httpx.AsyncClient) -> str:
     return "\n".join(lines) if lines else "Aucune métrique disponible."
 
 
+async def network_block(client: httpx.AsyncClient) -> str:
+    """Surveillance réseau active (sondes blackbox_exporter) : joignabilité,
+    internet, DNS, latence LAN, et liste des sondes en échec."""
+    try:
+        total = await _prom_query(client, 'count(probe_success{job=~"blackbox-.*"})')
+        up = await _prom_query(client, 'count(probe_success{job=~"blackbox-.*"} == 1)')
+        internet = await _prom_query(client, 'sum(probe_success{job="blackbox-icmp",scope="internet"})')
+        dns_lab = await _prom_query(client, 'probe_success{job="blackbox-dns",module="dns_lab"}')
+        rtt = await _prom_query(client, 'max(probe_icmp_duration_seconds{scope="lan",phase="rtt"})')
+        failing = await _prom_query(client, 'probe_success{job=~"blackbox-.*"} == 0')
+    except httpx.HTTPError:
+        return "Données indisponibles : Prometheus injoignable."
+    if not total:
+        return ("Aucune sonde réseau active (blackbox_exporter pas encore déployé "
+                "ou sans données).")
+    lines = [f"Sondes réseau OK : {int(up[0][1]) if up else 0}/{int(total[0][1])}."]
+    if internet:
+        lines.append("Internet : " + ("accessible" if internet[0][1] > 0 else "INACCESSIBLE") + ".")
+    if dns_lab:
+        lines.append("DNS *.lab.local : " + ("OK" if dns_lab[0][1] == 1 else "EN ÉCHEC") + ".")
+    if rtt:
+        lines.append(f"Latence LAN max : {round(rtt[0][1] * 1000)} ms.")
+    if failing:
+        names = ", ".join(m.get("instance", "?") for m, _ in failing[:8] if m.get("instance"))
+        lines.append(f"⚠️ Sondes en échec : {names}.")
+    else:
+        lines.append("Toutes les sondes répondent.")
+    return "\n".join(lines)
+
+
 # Aiguillage source_id → fetcher
 _FETCHERS = {
     "ghostfolio": ghostfolio_block,
     "alerts": alerts_block,
     "cluster": cluster_block,
     "metrics": metrics_block,
+    "network": network_block,
 }