feat(observability): add maintenance policy metrics

Prometheus: runs, duration, rows_deleted, config_changes; инкремент при CRUD и Execute.
Co-authored-by: Cursor <[email protected]>

internal/observability/maintenance_metrics.go

@@ -0,0 +1,72 @@
+package observability
+
+import (
+	"strconv"
+	"time"
+
+	"github.com/prometheus/client_golang/prometheus"
+	"github.com/prometheus/client_golang/prometheus/promauto"
+)
+
+var (
+	maintenancePolicyRuns = promauto.NewCounterVec(
+		prometheus.CounterOpts{
+			Namespace: namespace,
+			Name:      "maintenance_policy_runs_total",
+			Help:      "Maintenance policy executions by outcome.",
+		},
+		[]string{"policy_id", "action", "status", "dry_run"},
+	)
+
+	maintenancePolicyDuration = promauto.NewHistogramVec(
+		prometheus.HistogramOpts{
+			Namespace: namespace,
+			Name:      "maintenance_policy_duration_seconds",
+			Help:      "Maintenance policy execution duration.",
+			Buckets:   prometheus.ExponentialBuckets(0.05, 2, 12),
+		},
+		[]string{"policy_id", "action"},
+	)
+
+	maintenanceRowsDeleted = promauto.NewCounterVec(
+		prometheus.CounterOpts{
+			Namespace: namespace,
+			Name:      "maintenance_policy_rows_deleted_total",
+			Help:      "Rows deleted by maintenance cleanup policies.",
+		},
+		[]string{"policy_id"},
+	)
+
+	maintenanceConfigChanges = promauto.NewCounterVec(
+		prometheus.CounterOpts{
+			Namespace: namespace,
+			Name:      "maintenance_config_changes_total",
+			Help:      "Maintenance policy configuration changes from UI/API.",
+		},
+		[]string{"action"},
+	)
+)
+
+// RecordMaintenancePolicyRun updates run counters and histograms.
+func RecordMaintenancePolicyRun(policyID, action, status string, dryRun bool, duration time.Duration, rowsDeleted int64) {
+	if policyID == "" {
+		policyID = "unknown"
+	}
+	if action == "" {
+		action = "run"
+	}
+	dry := strconv.FormatBool(dryRun)
+	maintenancePolicyRuns.WithLabelValues(policyID, action, status, dry).Inc()
+	maintenancePolicyDuration.WithLabelValues(policyID, action).Observe(duration.Seconds())
+	if rowsDeleted > 0 && !dryRun {
+		maintenanceRowsDeleted.WithLabelValues(policyID).Add(float64(rowsDeleted))
+	}
+}
+
+// IncMaintenanceConfigChange increments config audit metric.
+func IncMaintenanceConfigChange(action string) {
+	if action == "" {
+		action = "unknown"
+	}
+	maintenanceConfigChanges.WithLabelValues(action).Inc()
+}