v1.1.3: surface daemon version + commit on maglev_info

Extend the existing maglev_info gauge with two more labels:
- version (build version, from -ldflags)
- commit (git short hash)

Mirrors nginx_ipng_stats-plugin's nginx_ipng_info pattern: a
label-only gauge value=1 carrying build metadata for Prometheus
to query and Grafana dashboards to render. Useful for spotting
version drift across the fleet with a single query, and for
populating the "Version" column of the Maglev Nodes table on
the global overview.

Existing label source_tag is preserved.

Plumbing: NewCollector / Register signatures gain version and
commit string parameters; main.go reads them from cmd.Version()
and cmd.Commit() (already imported as 'buildinfo').

internal/metrics/metrics.go

@@ -134,6 +134,8 @@ type Collector struct {
 	src       StateSource
 	vpp       VPPSource // optional; nil when VPP integration is disabled
 	sourceTag string
+	version   string
+	commit    string
 
 	maglevInfo     *prometheus.Desc
 	backendState   *prometheus.Desc
@@ -153,16 +155,18 @@ type Collector struct {
 
 // NewCollector creates a Collector backed by the given StateSource. vpp may
 // be nil when VPP integration is disabled; in that case vpp_* metrics are
-// simply not emitted.
-func NewCollector(src StateSource, vpp VPPSource, sourceTag string) *Collector {
+// simply not emitted. version and commit are surfaced via maglev_info labels.
+func NewCollector(src StateSource, vpp VPPSource, sourceTag, version, commit string) *Collector {
 	return &Collector{
 		src:       src,
 		vpp:       vpp,
 		sourceTag: sourceTag,
+		version:   version,
+		commit:    commit,
 		maglevInfo: prometheus.NewDesc(
 			"maglev_info",
 			"Static maglevd instance metadata. Always 1; metadata is conveyed via labels.",
-			[]string{"source_tag"}, nil,
+			[]string{"source_tag", "version", "commit"}, nil,
 		),
 		backendState: prometheus.NewDesc(
 			"maglev_backend_state",
@@ -240,7 +244,8 @@ func (c *Collector) Describe(ch chan<- *prometheus.Desc) {
 
 // Collect implements prometheus.Collector.
 func (c *Collector) Collect(ch chan<- prometheus.Metric) {
-	ch <- prometheus.MustNewConstMetric(c.maglevInfo, prometheus.GaugeValue, 1.0, c.sourceTag)
+	ch <- prometheus.MustNewConstMetric(c.maglevInfo, prometheus.GaugeValue, 1.0,
+		c.sourceTag, c.version, c.commit)
 
 	states := []health.State{
 		health.StateUnknown,
@@ -353,9 +358,10 @@ func (c *Collector) Collect(ch chan<- prometheus.Metric) {
 }
 
 // Register registers all metrics with the given registry. vpp may be nil
-// to disable VPP-related metrics.
-func Register(reg prometheus.Registerer, src StateSource, vpp VPPSource, sourceTag string) *Collector {
-	coll := NewCollector(src, vpp, sourceTag)
+// to disable VPP-related metrics. version / commit are surfaced via
+// maglev_info labels.
+func Register(reg prometheus.Registerer, src StateSource, vpp VPPSource, sourceTag, version, commit string) *Collector {
+	coll := NewCollector(src, vpp, sourceTag, version, commit)
 	reg.MustRegister(coll)
 	reg.MustRegister(ProbeTotal)
 	reg.MustRegister(ProbeDuration)