fix(sub): resolve a blank subId to no subscription

A subId is the only selector of a subscription's inbounds and external
links, so a blank one matched every client stored without a subId, as
clients embedded through inbounds/add or inbounds/import are. The
Telegram bot authorised a client by email and then looked its links up
by that blank subId, handing a bound user the working links of every
other subId-less client.

A blank subId now resolves to nothing in the subscription service, and
the bot builds a subId-less client's own links by email, as the panel's
client page does.

internal/sub/external_config.go

@@ -36,6 +36,9 @@ type expandedLink struct {
 // getClientExternalLinksBySubId returns active rows with owner state attached.
 // Consumers keep inactive owners as metadata but omit their link values.
 func (s *SubService) getClientExternalLinksBySubId(subId string) ([]externalLinkEntry, error) {
+	if strings.TrimSpace(subId) == "" {
+		return nil, nil
+	}
 	db := database.GetDB()
 	var recs []model.ClientRecord
 	if err := db.Where("sub_id = ?", subId).Find(&recs).Error; err != nil {