fix: worker 进程并发 double-close panic + 状态页连接语义重构 + 集群页骨架

- process: spawn 不再重复起 supervise goroutine（Restart 触发旧 supervise close doneCh 后再 close → panic）；新增 closeOnce/supervising 守卫；Start 首次起 supervise，重启循环在同一 goroutine 内

- httpapi: status 增加 connState（connected/connecting/failed/not_started/disabled），由 worker 日志探测真实 frps 连接（不再把本地 worker 状态误当远程 frps 状态）

- StatusView: 远程卡片主状态改为连接状态徽标；启停按钮标注为控制本地 frpc worker；本地转发区保留 worker 状态显示

- 新增 ClusterView 集群页骨架（M3 LB+健康检查载体）+ App.vue 导航接入

- render: bandwidthLimit 从 proxy 顶层移入 transport 段（frpc 0.61 正确 schema，修复真实连不上的 bug）

internal/httpapi/server.go

@@ -146,6 +146,9 @@ func (h *Handler) handleStatus(w http.ResponseWriter, r *http.Request) {
 		Status   process.Status  `json:"process"`
 		HasProc  bool            `json:"hasProcess"`
 		Forwards []store.Forward `json:"forwards"`
+		// ConnState is the derived frps connection state:
+		// connected | connecting | failed | not_started | disabled.
+		ConnState string `json:"connState"`
 	}
 
 	profiles := make([]profileStatus, 0, len(remotes))
@@ -158,6 +161,7 @@ func (h *Handler) handleStatus(w http.ResponseWriter, r *http.Request) {
 		fwd, _ := h.Store.LinksForRemote(rv.Name)
 		profiles = append(profiles, profileStatus{
 			Name: rv.Name, Enabled: rv.Enabled, Status: st, HasProc: has, Forwards: fwd,
+			ConnState: connStateOf(h.Process.LogPath(rv.Name), rv.Enabled, st),
 		})
 	}
 
@@ -204,6 +208,49 @@ func (h *Handler) handleStatus(w http.ResponseWriter, r *http.Request) {
 	writeJSON(w, http.StatusOK, resp)
 }
 
+// connStateOf derives the frps connection state from the local worker process
+// state plus a probe of its log. We never control the remote frps: the worker is
+// our local frpc; "connected" means frpc has successfully logged in to frps.
+// - disabled      -> remote disabled, worker not started
+// - running+login -> frpc logged in to frps (connected)
+// - running       -> frpc up but not yet logged in (connecting)
+// - starting/restarting -> connecting
+// - crashed/exit nonzero -> failed
+// - stopped clean / no worker -> not_started
+func connStateOf(workerLog string, enabled bool, st process.Status) string {
+	if !enabled {
+		return "disabled"
+	}
+	switch st.State {
+	case "running":
+		tail, _ := tailFile(workerLog, 64*1024)
+		if tail != "" {
+			// frpc prints "login to server success" once the control link is up.
+			if strings.Contains(tail, "login to server success") ||
+				strings.Contains(tail, "start proxy success") {
+				return "connected"
+			}
+			if strings.Contains(tail, "login to server error") ||
+				strings.Contains(tail, "connect to server error") ||
+				strings.Contains(tail, "connect server error") {
+				return "failed"
+			}
+		}
+		return "connecting"
+	case "starting", "restarting":
+		return "connecting"
+	case "crashed":
+		return "failed"
+	case "stopped":
+		if st.ExitCode != 0 || st.Err != "" {
+			return "failed"
+		}
+		return "not_started"
+	default:
+		return "not_started"
+	}
+}
+
 func methodNotAllowed(w http.ResponseWriter) {
 	http.Error(w, "method not allowed", http.StatusMethodNotAllowed)
 }