feat: unibus_exporter — daemon que sondea /healthz del cluster unibus y empuja estado+posture a VictoriaMetrics

Compone parse_unibus_health + format_prom_exposition + push_prom_remote del registry
(grupo fleet-metrics). Un solo exporter scrapea los 3 nodos por IP pública con la CA
del cluster; labels node/instance por serie. Config JSON con secretos fuera de argv.
Incluye systemd unit y unibus.example.json.

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

unibus.example.json

@@ -0,0 +1,14 @@
+{
+  "nodes": [
+    { "name": "magnus",   "url": "https://135.125.201.30:8470/healthz" },
+    { "name": "homer",    "url": "https://141.94.69.66:8470/healthz" },
+    { "name": "datardos", "url": "https://51.91.100.142:8470/healthz" }
+  ],
+  "ca_cert_path": "/etc/unibus-exporter/ca.crt",
+  "hub_url": "http://127.0.0.1:8428/api/v1/import/prometheus",
+  "user": "",
+  "pass": "",
+  "interval_sec": 15,
+  "timeout_sec": 8,
+  "labels": { "job": "unibus_exporter" }
+}