Добавлены метрики Prometheus и дашборды Grafana (этап 2.5)

Все три Go-сервиса (ingest, device-control, rule-engine) отдают
/metrics в формате Prometheus: счётчики MQTT/RabbitMQ/ClickHouse
операций, гистограммы длительности батч-флашей и диспатча правил,
переходы устройств online/offline. Добавлены сервисы prometheus и
grafana в docker-compose с провижининг конфигом (datasource +
два готовых дашборда: "Ingest & Telemetry" и "Automation & Devices").

services/rule-engine-service/internal/metrics/metrics.go

@@ -0,0 +1,37 @@
+// Package metrics defines rule-engine-service's Prometheus metrics.
+// Registered automatically (via promauto) into the default registry on
+// import; served by main.go's dedicated metrics HTTP server.
+package metrics
+
+import (
+	"github.com/prometheus/client_golang/prometheus"
+	"github.com/prometheus/client_golang/prometheus/promauto"
+)
+
+var (
+	ReadingsConsumed = promauto.NewCounter(prometheus.CounterOpts{
+		Name: "rule_engine_readings_consumed_total",
+		Help: "Total number of telemetry.new_reading events consumed from RabbitMQ.",
+	})
+
+	RulesMatched = promauto.NewCounter(prometheus.CounterOpts{
+		Name: "rule_engine_rules_matched_total",
+		Help: "Total number of rule conditions that evaluated true and were dispatched.",
+	})
+
+	RulesTriggered = promauto.NewCounterVec(prometheus.CounterOpts{
+		Name: "rule_engine_rules_triggered_total",
+		Help: "Total number of rule dispatch attempts, by action type and outcome.",
+	}, []string{"action_type", "outcome"})
+
+	DispatchDuration = promauto.NewHistogramVec(prometheus.HistogramOpts{
+		Name:    "rule_engine_dispatch_duration_seconds",
+		Help:    "Duration of the gRPC/HTTP call to device-control-service, by action type.",
+		Buckets: prometheus.DefBuckets,
+	}, []string{"action_type"})
+
+	CacheRefreshes = promauto.NewCounterVec(prometheus.CounterOpts{
+		Name: "rule_engine_cache_refresh_total",
+		Help: "Total number of automation_rules cache refreshes from PostgreSQL, by outcome.",
+	}, []string{"outcome"})
+)