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

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

server/websocket/handler.go

@@ -0,0 +1,34 @@
+package websocket
+
+import (
+	"log"
+	"net/http"
+
+	"github.com/gorilla/websocket"
+)
+
+var upgrader = websocket.Upgrader{
+	ReadBufferSize:  1024,
+	WriteBufferSize: 4096,
+	CheckOrigin:    func(r *http.Request) bool { return true },
+}
+
+func Handler(hub *Hub) http.HandlerFunc {
+	return func(w http.ResponseWriter, r *http.Request) {
+		conn, err := upgrader.Upgrade(w, r, nil)
+		if err != nil {
+			log.Printf("[ws] upgrade: %v", err)
+			return
+		}
+		hub.Register(conn)
+		defer func() {
+			hub.Unregister(conn)
+			conn.Close()
+		}()
+		for {
+			if _, _, err := conn.ReadMessage(); err != nil {
+				break
+			}
+		}
+	}
+}