feat: auto-trunk creation, SIP gateway in metrics, gateway WS broadcast

- SIPGateway field in NodeMetric model
- HasNode() engine method
- OnNewNode callback in NATS subscriber
- Auto-create balance trunk from new node metric
- BroadcastGatewayEvent on WS hub
- Gateway status indicators in trunks UI (green/red/gray)
- SPA fallback for frontend routing

internal/api/router.go

@@ -8,6 +8,7 @@ import (
 	"github.com/pulse-lets-go/internal/config"
 	"github.com/pulse-lets-go/internal/engine"
 	"github.com/pulse-lets-go/internal/esl"
+	"github.com/pulse-lets-go/internal/models"
 )
 
 // API — главная структура HTTP API, агрегирует все зависимости.
@@ -127,6 +128,19 @@ func corsMiddleware(next http.Handler) http.Handler {
 	})
 }
 
+// BroadcastGatewayEvent транслирует статус gateway всем WS-клиентам.
+func (a *API) BroadcastGatewayEvent(gatewayName, trunkID, status string) {
+	msg := &models.WsMetricsMessage{
+		Type: "gateway_update",
+		Payload: map[string]string{
+			"gateway":  gatewayName,
+			"trunk_id": trunkID,
+			"status":   status,
+		},
+	}
+	a.wsHub.broadcast(msg)
+}
+
 // decodeJSON декодирует тело запроса в структуру v.
 func decodeJSON(r *http.Request, v interface{}) error {
 	defer r.Body.Close()