feat(monitoring): add node/tunnel metrics, service monitors, and health checks

- Add NodeMetric/TunnelMetric/ServiceMonitor models and repository methods
- Implement metrics ingestion service with per-minute bucket aggregation
- Add health checker for node connectivity monitoring
- Wire node metrics from WebSocket SystemInfo messages
- Add tunnel metrics ingestion from flow upload endpoint
- Create monitoring REST API endpoints for nodes, tunnels, services
- Implement service monitor CRUD and execution (TCP/ICMP checks)
- Add MonitorPermission for non-admin access control
- Create frontend monitor page with node/tunnel/service views
- Add tunnel metrics ingestion from agent flow reports
- Include schema migration for tunnel_metric unique index
- Fix tunnel entry port conflict validation to use transaction

Entire-Checkpoint: 030821a7c8e3

go-backend/internal/http/handler/tunnel_metrics_ingestion.go

@@ -0,0 +1,111 @@
+package handler
+
+import (
+	"log"
+	"strings"
+	"time"
+
+	"go-backend/internal/store/model"
+)
+
+type tunnelTrafficDelta struct {
+	bytesIn  int64
+	bytesOut int64
+}
+
+func unixMilliBucketMinute(nowMs int64) int64 {
+	if nowMs <= 0 {
+		return 0
+	}
+	const minuteMs = int64(time.Minute / time.Millisecond)
+	return nowMs - (nowMs % minuteMs)
+}
+
+func (h *Handler) recordTunnelMetricsFromFlowItems(nodeID int64, items []flowItem, nowMs int64) {
+	if h == nil || h.repo == nil {
+		return
+	}
+	if nodeID <= 0 || len(items) == 0 {
+		return
+	}
+
+	bucketTs := unixMilliBucketMinute(nowMs)
+	if bucketTs <= 0 {
+		return
+	}
+
+	forwardDeltas := make(map[int64]tunnelTrafficDelta)
+	for _, item := range items {
+		name := strings.TrimSpace(item.N)
+		if name == "" || name == "web_api" {
+			continue
+		}
+		forwardID, _, _, ok := parseFlowServiceIDs(name)
+		if !ok {
+			continue
+		}
+		if item.D == 0 && item.U == 0 {
+			continue
+		}
+		d := forwardDeltas[forwardID]
+		d.bytesIn += item.D
+		d.bytesOut += item.U
+		forwardDeltas[forwardID] = d
+	}
+	if len(forwardDeltas) == 0 {
+		return
+	}
+
+	forwardIDs := make([]int64, 0, len(forwardDeltas))
+	for id := range forwardDeltas {
+		forwardIDs = append(forwardIDs, id)
+	}
+
+	forwardTunnelMap, err := h.repo.MapForwardIDsToTunnelIDs(forwardIDs)
+	if err != nil {
+		log.Printf("monitoring write skipped op=tunnel_metric.map_forward_to_tunnel node_id=%d err=%v", nodeID, err)
+		return
+	}
+	if len(forwardTunnelMap) == 0 {
+		return
+	}
+
+	tunnelAgg := make(map[int64]tunnelTrafficDelta)
+	for forwardID, delta := range forwardDeltas {
+		tunnelID := forwardTunnelMap[forwardID]
+		if tunnelID <= 0 {
+			continue
+		}
+		a := tunnelAgg[tunnelID]
+		a.bytesIn += delta.bytesIn
+		a.bytesOut += delta.bytesOut
+		tunnelAgg[tunnelID] = a
+	}
+	if len(tunnelAgg) == 0 {
+		return
+	}
+
+	metrics := make([]*model.TunnelMetric, 0, len(tunnelAgg))
+	for tunnelID, delta := range tunnelAgg {
+		if delta.bytesIn == 0 && delta.bytesOut == 0 {
+			continue
+		}
+		metrics = append(metrics, &model.TunnelMetric{
+			TunnelID:     tunnelID,
+			NodeID:       nodeID,
+			Timestamp:    bucketTs,
+			BytesIn:      delta.bytesIn,
+			BytesOut:     delta.bytesOut,
+			Connections:  0,
+			Errors:       0,
+			AvgLatencyMs: 0,
+		})
+	}
+	if len(metrics) == 0 {
+		return
+	}
+
+	if err := h.repo.UpsertTunnelMetricBuckets(metrics); err != nil {
+		log.Printf("monitoring write failed op=tunnel_metric.upsert_buckets node_id=%d bucket_ts=%d count=%d err=%v", nodeID, bucketTs, len(metrics), err)
+	}
+}