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/web/entity/entity.go

@@ -10,6 +10,7 @@ import (
 	"time"
 
 	"github.com/mhsanaei/3x-ui/v3/internal/util/common"
+	"github.com/mhsanaei/3x-ui/v3/internal/util/cronspec"
 )
 
 type Msg struct {
@@ -352,6 +353,19 @@ func (s *AllSetting) CheckValid() error {
 		s.SubClashPath += "/"
 	}
 
+	for _, sched := range []struct{ name, spec string }{
+		{"tgRunTime", s.TgRunTime},
+		{"discordRunTime", s.DiscordRunTime},
+		{"ldapSyncCron", s.LdapSyncCron},
+	} {
+		if strings.TrimSpace(sched.spec) == "" {
+			continue
+		}
+		if _, err := cronspec.Parse(sched.spec); err != nil {
+			return common.NewError(sched.name+":", err)
+		}
+	}
+
 	if err := checkIPOrCIDRList(s.TrustedProxyCIDRs, "trusted proxy CIDR is not valid:"); err != nil {
 		return err
 	}