feat(server): UDP listener, hub WebSocket, Gauges Prometheus

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

server/transport/udp.go

@@ -0,0 +1,43 @@
+package transport
+
+import (
+	"encoding/json"
+	"log"
+	"net"
+
+	"github.com/user/nanometrics/server/models"
+)
+
+func StartUDP(addr string, handler func(*models.AgentMetrics)) error {
+	conn, err := net.ListenPacket("udp", addr)
+	if err != nil {
+		return err
+	}
+	log.Printf("[udp] écoute sur %s", addr)
+	go func() {
+		buf := make([]byte, 65535)
+		for {
+			n, _, err := conn.ReadFrom(buf)
+			if err != nil {
+				log.Printf("[udp] erreur lecture: %v", err)
+				continue
+			}
+			data := make([]byte, n)
+			copy(data, buf[:n])
+			go processUDP(data, handler)
+		}
+	}()
+	return nil
+}
+
+func processUDP(data []byte, handler func(*models.AgentMetrics)) {
+	var m models.AgentMetrics
+	if err := json.Unmarshal(data, &m); err != nil {
+		log.Printf("[udp] JSON invalide: %v", err)
+		return
+	}
+	if m.Hostname == "" {
+		return
+	}
+	handler(&m)
+}