feat: add route_fallbacks metric to Prometheus and Zabbix monitoring

- Prometheus: new pulse_route_fallbacks_total counter
- Zabbix: extend response with route_requests_total, route_fallbacks_total, uptime_seconds
- Docs: update Prometheus metrics table and Zabbix response example

docs/api.md

@@ -216,7 +216,10 @@ Use `X-API-Key` header (not JWT).
       "{#IS_STALE}": false,
       "{#SECONDS_AGO}": 3.0
     }
-  ]
+  ],
+  "route_requests_total": 5000,
+  "route_fallbacks_total": 42,
+  "uptime_seconds": 7200
 }
 ```
 
@@ -225,6 +228,7 @@ Use `X-API-Key` header (not JWT).
 | Метрика | Type | Labels |
 |---------|------|--------|
 | `pulse_route_requests_total` | counter | – |
+| `pulse_route_fallbacks_total` | counter | – |
 | `pulse_nodes_total` | gauge | – |
 | `pulse_nodes_healthy` | gauge | – |
 | `pulse_uptime_seconds` | gauge | – |

internal/api/monitoring.go

@@ -29,7 +29,13 @@ func (a *API) handleZabbix(w http.ResponseWriter, r *http.Request) {
 		})
 	}
 
-	writeJSON(w, http.StatusOK, models.ZabbixResponse{Data: data})
+	stats := a.engine.GetHealthStats()
+	writeJSON(w, http.StatusOK, models.ZabbixResponse{
+		Data:           data,
+		RouteRequests:  stats.RouteRequests,
+		RouteFallbacks: stats.RouteFallbacks,
+		UptimeSeconds:  stats.UptimeSeconds,
+	})
 }
 
 // handlePrometheus — GET /api/monitoring/prometheus — text/plain метрики для Prometheus.
@@ -52,6 +58,10 @@ func (a *API) handlePrometheus(w http.ResponseWriter, r *http.Request) {
 	fmt.Fprintf(&sb, "# TYPE pulse_nodes_healthy gauge\n")
 	fmt.Fprintf(&sb, "pulse_nodes_healthy %d\n", stats.HealthyNodes)
 
+	fmt.Fprintf(&sb, "# HELP pulse_route_fallbacks_total Total number of fallback route requests.\n")
+	fmt.Fprintf(&sb, "# TYPE pulse_route_fallbacks_total counter\n")
+	fmt.Fprintf(&sb, "pulse_route_fallbacks_total %d\n", stats.RouteFallbacks)
+
 	fmt.Fprintf(&sb, "# HELP pulse_uptime_seconds Uptime in seconds.\n")
 	fmt.Fprintf(&sb, "# TYPE pulse_uptime_seconds gauge\n")
 	fmt.Fprintf(&sb, "pulse_uptime_seconds %d\n", stats.UptimeSeconds)

internal/models/types.go

@@ -242,6 +242,9 @@ type ZabbixNode struct {
 // ZabbixResponse — ответ на запрос Zabbix LLD.
 type ZabbixResponse struct {
 	Data             []ZabbixNode `json:"data"`
+	RouteRequests    int64        `json:"route_requests_total"`
+	RouteFallbacks   int64        `json:"route_fallbacks_total"`
+	UptimeSeconds    int64        `json:"uptime_seconds"`
 }
 
 // --- Balancer ---