fix(settings): accept five-field crontab for report and LDAP schedules

The panel scheduler runs WithSeconds(), whose parser rejects a standard
five-field crontab such as "30 8 * * *". An admin who typed one into the
Telegram/Discord notify time or the LDAP sync schedule saved it without
error, AddJob then failed at startup, and the job silently never ran.

Admin-typed schedules now go through internal/util/cronspec, which takes
an optional seconds column plus the @descriptors and hands the scheduler
a parsed cron.Schedule. CheckValid rejects an unparseable schedule on
save, and a stored legacy value falls back to the job's default instead
of dropping the job.

internal/util/cronspec/cronspec.go

@@ -0,0 +1,24 @@
+// Package cronspec parses the cron schedules an admin types into the settings.
+package cronspec
+
+import (
+	"strings"
+
+	"github.com/robfig/cron/v3"
+
+	"github.com/mhsanaei/3x-ui/v3/internal/util/common"
+)
+
+// The panel scheduler runs WithSeconds(), whose parser rejects five-field crontab,
+// so admin schedules are parsed here with the seconds column optional.
+var parser = cron.NewParser(
+	cron.SecondOptional | cron.Minute | cron.Hour | cron.Dom | cron.Month | cron.Dow | cron.Descriptor,
+)
+
+func Parse(spec string) (cron.Schedule, error) {
+	schedule, err := parser.Parse(strings.TrimSpace(spec))
+	if err != nil {
+		return nil, common.NewErrorf("cron schedule <%v> is not valid: %v", spec, err)
+	}
+	return schedule, nil
+}

internal/util/cronspec/cronspec_test.go

@@ -0,0 +1,47 @@
+package cronspec
+
+import (
+	"strings"
+	"testing"
+	"time"
+)
+
+// #1648 upstream: the panel's scheduler runs WithSeconds(), whose parser refused
+// a standard five-field crontab, so an admin's "30 8 * * *" never fired.
+func TestParseNextFire(t *testing.T) {
+	from := time.Date(2026, 10, 11, 7, 0, 0, 0, time.UTC)
+	cases := []struct {
+		spec string
+		want time.Time
+	}{
+		{"30 8 * * *", time.Date(2026, 10, 11, 8, 30, 0, 0, time.UTC)},
+		{" 15 30 8 * * * ", time.Date(2026, 10, 11, 8, 30, 15, 0, time.UTC)},
+		{"@daily", time.Date(2026, 10, 12, 0, 0, 0, 0, time.UTC)},
+		{"@every 90m", from.Add(90 * time.Minute)},
+	}
+	for _, c := range cases {
+		t.Run(c.spec, func(t *testing.T) {
+			schedule, err := Parse(c.spec)
+			if err != nil {
+				t.Fatalf("Parse(%q): %v", c.spec, err)
+			}
+			if got := schedule.Next(from); !got.Equal(c.want) {
+				t.Errorf("Parse(%q).Next = %v, want %v", c.spec, got, c.want)
+			}
+		})
+	}
+}
+
+func TestParseRejects(t *testing.T) {
+	for _, spec := range []string{"", "   ", "every day", "61 * * * *", "* * * *"} {
+		t.Run(spec, func(t *testing.T) {
+			_, err := Parse(spec)
+			if err == nil {
+				t.Fatalf("Parse(%q): want error, got nil", spec)
+			}
+			if !strings.Contains(err.Error(), "cron schedule") {
+				t.Errorf("Parse(%q) error = %q, want it to name the cron schedule", spec, err)
+			}
+		})
+	}
+}