feat(ws): A3 WebSocket 统一连接管理 — 心跳/注册表/监控/优雅关闭

- 新增 pkg/wshub/manager.go 统一 WebSocket 连接管理器 (WSManager)
- 6 个 WebSocket handler 全部迁移: WebShell/kubectl/PodExec/Audit/Metrics/Pipeline
- 心跳机制: ping(30s) + pong handler + read deadline(60s) 自动检测死连接
- 连接注册表: 元数据(类型/用户/远程地址/连接时间/最后活跃)
- 每用户连接限制 MaxConnsPerUser=15 防资源耗尽
- 监控端点: GET /api/v1/ws/stats + GET /api/v1/ws/connections
- 优雅关闭: CloseAll() 发送 CloseGoingAway 帧并关闭所有连接
- 消除 3 个重复 websocket.Upgrader 变量统一为 WSManager 内部 upgrader
- 6/6 A3 测试通过, 17/17 回归测试通过

backend/controller/kubectl_shell.go

@@ -12,8 +12,10 @@ import (
 	"strconv"
 	"syscall"
 
+	"ezops/middleware"
 	"ezops/model"
 	"ezops/pkg/toolinstaller"
+	"ezops/pkg/wshub"
 
 	"github.com/creack/pty"
 	"github.com/gin-gonic/gin"
@@ -23,13 +25,14 @@ import (
 
 // KubectlShellHandler kubectl WebSocket 终端处理（PTY 模式）
 type KubectlShellHandler struct {
-	db             *gorm.DB
-	toolInstaller  *toolinstaller.ToolInstaller
+	db            *gorm.DB
+	toolInstaller *toolinstaller.ToolInstaller
+	wsMgr         *wshub.WSManager
 }
 
 // NewKubectlShellHandler creates handler
-func NewKubectlShellHandler(db *gorm.DB, ti *toolinstaller.ToolInstaller) *KubectlShellHandler {
-	return &KubectlShellHandler{db: db, toolInstaller: ti}
+func NewKubectlShellHandler(db *gorm.DB, ti *toolinstaller.ToolInstaller, wsMgr *wshub.WSManager) *KubectlShellHandler {
+	return &KubectlShellHandler{db: db, toolInstaller: ti, wsMgr: wsMgr}
 }
 
 // wsWriter wraps a websocket.Conn as an io.Writer (each write = one WSMessage)
@@ -68,12 +71,16 @@ func (h *KubectlShellHandler) Terminal(c *gin.Context) {
 		return
 	}
 
-	conn, err := upgrader.Upgrade(c.Writer, c.Request, nil)
+	userID := middleware.GetUserID(c)
+	username := middleware.GetUsername(c)
+
+	conn, info, err := h.wsMgr.Upgrade(c, wshub.TypeKubectl, userID, username)
 	if err != nil {
 		log.Printf("[KubectlShell] WebSocket upgrade failed: %v", err)
 		return
 	}
-	defer conn.Close()
+	defer h.wsMgr.Unregister(info)
+	h.wsMgr.StartHeartbeat(conn, info)
 
 	// Write kubeconfig to a temp file (isolated per session)
 	tmpFile, err := os.CreateTemp("", "kubeconfig-*.yaml")