add POST /logs installer log relay to VictoriaLogs

A host being PXE-discovered or installed is not in Kubernetes, so vlagent
cannot collect its logs and a failed install leaves no record; the installer
environment has no internal-CA trust or credentials for the HTTPS log ingest,
and bootapi is already the plain-HTTP broker it can reach.

- add POST /logs, token-guarded like POST /provisioned, relaying ndjson to
  vlinsert's jsonline endpoint keyed on serial+phase
- stamp observed source IP and resolved NetBox device name into extra_fields
- return 202 on a sink failure so logs never block an install
- add BOOTAPI_VLINSERT_URL/_TIMEOUT and bootapi_log_relay metrics

internal/server/metrics.go

@@ -28,6 +28,8 @@ type metrics struct {
 	netboxLookups  *prometheus.CounterVec // by field,result
 	netboxDuration *prometheus.HistogramVec
 	provisioned    *prometheus.CounterVec // by result
+	logRelay       *prometheus.CounterVec // by result
+	logLines       prometheus.Counter
 	ipxeGated      prometheus.Counter
 }
 
@@ -56,12 +58,20 @@ func newMetrics(cache cacheStats, git gitStats) *metrics {
 			Name: "bootapi_provisioned_total",
 			Help: "Provisioned callbacks, by result (ok|unauthorized|notfound|error|disabled).",
 		}, []string{"result"}),
+		logRelay: prometheus.NewCounterVec(prometheus.CounterOpts{
+			Name: "bootapi_log_relay_total",
+			Help: "Installer log batches relayed to VictoriaLogs, by result (ok|error|unauthorized|disabled).",
+		}, []string{"result"}),
+		logLines: prometheus.NewCounter(prometheus.CounterOpts{
+			Name: "bootapi_log_relay_lines_total",
+			Help: "Installer log lines successfully relayed to VictoriaLogs.",
+		}),
 		ipxeGated: prometheus.NewCounter(prometheus.CounterOpts{
 			Name: "bootapi_ipxe_gated_total",
 			Help: "Known hosts served the local-boot fallback because pxe_enabled=false.",
 		}),
 	}
-	reg.MustRegister(m.httpRequests, m.renders, m.netboxLookups, m.netboxDuration, m.provisioned, m.ipxeGated)
+	reg.MustRegister(m.httpRequests, m.renders, m.netboxLookups, m.netboxDuration, m.provisioned, m.logRelay, m.logLines, m.ipxeGated)
 	if cache != nil {
 		reg.MustRegister(newCacheCollector(cache))
 	}