fix(nodes): stop a restarting panel from reporting itself as down

Adding a node fails right after that node's panel restarts. nodes/add
probes the node's /panel/api/server/status first, and that endpoint
returns whatever the @2s ticker last sampled - nil until the first tick
lands, so the master reads a healthy panel as unreachable and rejects it
with "Add node (remote returned success=false: )", an error whose
message is empty because the node answered success with a null obj.

The window is far wider than one tick: GetStatus resolved the public
IPv4/IPv6 addresses inline and held s.mu across every lookup, so a box
with no IPv6 route spent 3s per service - about 15s of nil status after
each restart, and the same stall on a fresh panel's first sample.

- status now answers from CurrentStatus, which samples on demand when
  the ticker has not run yet instead of returning a null obj
- the public-IP lookups run in the background and outside s.mu, so a
  status sample never waits on them
- probe tells "no status yet" apart from a genuine success=false, so the
  master's error says something when it meets an older node

internal/web/service/node_probe_unsampled_test.go

@@ -0,0 +1,48 @@
+package service
+
+import (
+	"context"
+	"net/http"
+	"net/http/httptest"
+	"net/url"
+	"strconv"
+	"strings"
+	"testing"
+
+	"github.com/mhsanaei/3x-ui/v3/internal/database/model"
+)
+
+// An older node answers success with a null obj while its status is unsampled,
+// which used to surface as "success=false: " with nothing after the colon.
+func TestProbeNamesANodeThatHasNoStatusYet(t *testing.T) {
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, _ *http.Request) {
+		w.Header().Set("Content-Type", "application/json")
+		_, _ = w.Write([]byte(`{"success":true,"msg":"","obj":null}`))
+	}))
+	defer srv.Close()
+
+	u, err := url.Parse(srv.URL)
+	if err != nil {
+		t.Fatalf("parse url: %v", err)
+	}
+	port, err := strconv.Atoi(u.Port())
+	if err != nil {
+		t.Fatalf("parse port: %v", err)
+	}
+	n := &model.Node{
+		Id: 1, Name: "cold", Scheme: "http", Address: u.Hostname(), Port: port,
+		BasePath: "/", Enable: true, AllowPrivateAddress: true, TlsVerifyMode: "skip",
+	}
+
+	svc := &NodeService{}
+	patch, err := svc.Probe(context.Background(), n)
+	if err == nil {
+		t.Fatal("Probe accepted a status response with no obj, want an error")
+	}
+	if strings.Contains(patch.LastError, "success=false") {
+		t.Fatalf("LastError = %q, want the missing status named instead of a bare success=false", patch.LastError)
+	}
+	if !strings.Contains(patch.LastError, "no status yet") {
+		t.Fatalf("LastError = %q, want it to say the remote reported no status yet", patch.LastError)
+	}
+}