feat: implement system metrics and fix monitoring charts

Added /api/system/metrics with CPU/Mem/Disk/Load data using gopsutil. Updated Hub to track active WebSocket listeners. Verified log format for monitoring charts.

internal/server/websocket.go

@@ -4,6 +4,7 @@ import (
 	"log"
 	"net/http"
 	"sync"
+	"sync/atomic"
 
 	"github.com/gin-gonic/gin"
 	"github.com/gorilla/websocket"
@@ -18,11 +19,12 @@ var upgrader = websocket.Upgrader{
 }
 
 type Hub struct {
-	clients    map[*websocket.Conn]bool
-	broadcast  chan interface{}
-	register   chan *websocket.Conn
-	unregister chan *websocket.Conn
-	mu         sync.Mutex
+	clients     map[*websocket.Conn]bool
+	broadcast   chan interface{}
+	register    chan *websocket.Conn
+	unregister  chan *websocket.Conn
+	mu          sync.Mutex
+	clientCount int32
 }
 
 func NewHub() *Hub {
@@ -40,6 +42,7 @@ func (h *Hub) Run() {
 		case client := <-h.register:
 			h.mu.Lock()
 			h.clients[client] = true
+			atomic.AddInt32(&h.clientCount, 1)
 			h.mu.Unlock()
 			log.Println("WebSocket client registered")
 		case client := <-h.unregister:
@@ -47,6 +50,7 @@ func (h *Hub) Run() {
 			if _, ok := h.clients[client]; ok {
 				delete(h.clients, client)
 				client.Close()
+				atomic.AddInt32(&h.clientCount, -1)
 			}
 			h.mu.Unlock()
 			log.Println("WebSocket client unregistered")
@@ -58,6 +62,7 @@ func (h *Hub) Run() {
 					log.Printf("WebSocket error: %v", err)
 					client.Close()
 					delete(h.clients, client)
+					atomic.AddInt32(&h.clientCount, -1)
 				}
 			}
 			h.mu.Unlock()
@@ -65,6 +70,10 @@ func (h *Hub) Run() {
 	}
 }
 
+func (h *Hub) GetClientCount() int {
+	return int(atomic.LoadInt32(&h.clientCount))
+}
+
 func (s *Server) handleWebSocket(c *gin.Context) {
 	conn, err := upgrader.Upgrade(c.Writer, c.Request, nil)
 	if err != nil {