feat: add controller sysinfo metrics (unpoller#927)

- Add Sysinfo collection from stat/sysinfo endpoint
- Export controller_info, uptime, update_available, data retention, ports
- Hostname fallback: name, then site_name when API omits hostname
- Apply site name override to Sysinfo for remote/cloud
- Add Discover/Discoverer for endpoint discovery
- Require unpoller/unifi v5.15.0

Co-authored-by: Cursor <cursoragent@cursor.com>

pkg/inputunifi/collector.go

@@ -198,6 +198,14 @@ func (u *InputUnifi) pollController(c *Controller) (*poller.Metrics, error) {
 		u.LogDebugf("Found %d WAN configuration entries", len(m.WANConfigs))
 	}
 
+	// Get controller system info (UniFi OS only)
+	if m.Sysinfos, err = c.Unifi.GetSysinfo(sites); err != nil {
+		// Don't fail collection if sysinfo fails - older controllers may not have this endpoint
+		u.LogDebugf("unifi.GetSysinfo(%s): %v (continuing)", c.URL, err)
+	} else {
+		u.LogDebugf("Found %d Sysinfo entries", len(m.Sysinfos))
+	}
+
 	return u.augmentMetrics(c, m), nil
 }
 
@@ -397,6 +405,10 @@ func (u *InputUnifi) augmentMetrics(c *Controller, metrics *Metrics) *poller.Met
 		m.WANConfigs = append(m.WANConfigs, wanConfig)
 	}
 
+	for _, sysinfo := range metrics.Sysinfos {
+		m.Sysinfos = append(m.Sysinfos, sysinfo)
+	}
+
 	// Apply default_site_name_override to all metrics if configured.
 	// This must be done AFTER all metrics are added to m, so everything is included.
 	// This allows us to use the console name for Cloud Gateways while keeping
@@ -502,6 +514,15 @@ func applySiteNameOverride(m *poller.Metrics, overrideName string) {
 		}
 	}
 
+	// Apply to sysinfo (controller metrics)
+	for i := range m.Sysinfos {
+		if s, ok := m.Sysinfos[i].(*unifi.Sysinfo); ok {
+			if isDefaultSiteName(s.SiteName) {
+				s.SiteName = overrideName
+			}
+		}
+	}
+
 	// Apply to WAN configs
 	for i := range m.WANConfigs {
 		if wanConfig, ok := m.WANConfigs[i].(*unifi.WANEnrichedConfiguration); ok {