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/device-control-service/internal/metrics/metrics.go

@@ -0,0 +1,32 @@
+// Package metrics defines device-control-service's Prometheus metrics.
+// Registered automatically (via promauto) into the default registry on
+// import; served alongside the command HTTP API's /metrics route.
+package metrics
+
+import (
+	"github.com/prometheus/client_golang/prometheus"
+	"github.com/prometheus/client_golang/prometheus/promauto"
+)
+
+var (
+	CommandsTotal = promauto.NewCounterVec(prometheus.CounterOpts{
+		Name: "device_control_commands_total",
+		Help: "Total number of TurnOn/TurnOff/SetLevel commands dispatched, by action and outcome.",
+	}, []string{"action", "outcome"})
+
+	CommandDuration = promauto.NewHistogramVec(prometheus.HistogramOpts{
+		Name:    "device_control_command_duration_seconds",
+		Help:    "Duration of a command dispatch (Redis desired_state patch + MQTT publish), by action.",
+		Buckets: prometheus.DefBuckets,
+	}, []string{"action"})
+
+	MQTTEventsTotal = promauto.NewCounterVec(prometheus.CounterOpts{
+		Name: "device_control_mqtt_events_total",
+		Help: "Total number of telemetry/ack messages received, by event type and outcome.",
+	}, []string{"event_type", "outcome"})
+
+	HealthTransitionsTotal = promauto.NewCounterVec(prometheus.CounterOpts{
+		Name: "device_control_health_transitions_total",
+		Help: "Total number of device online/offline transitions detected.",
+	}, []string{"direction"})
+)