feat(sub): per-client external links and remote subscriptions

Add a Links tab to the client form for attaching third-party share
links and remote subscription URLs per client. They are merged into
the client's raw/JSON/Clash subscription output: links are emitted
verbatim and parsed for JSON/Clash; subscription URLs are fetched
(cached, with a short timeout) and their configs merged in.

i18n keys added across all 13 locales.

internal/web/service/client_crud.go

@@ -407,6 +407,9 @@ func (s *ClientService) Delete(inboundSvc *InboundService, id int, keepTraffic b
 	if err := db.Where("client_id = ?", id).Delete(&model.ClientInbound{}).Error; err != nil {
 		return needRestart, err
 	}
+	if err := db.Where("client_id = ?", id).Delete(&model.ClientExternalLink{}).Error; err != nil {
+		return needRestart, err
+	}
 	if !keepTraffic && existing.Email != "" {
 		if err := db.Where("email = ?", existing.Email).Delete(&xray.ClientTraffic{}).Error; err != nil {
 			return needRestart, err

internal/web/service/client_external_link.go

@@ -0,0 +1,103 @@
+package service
+
+import (
+	"net/url"
+	"strings"
+
+	"github.com/mhsanaei/3x-ui/v3/internal/database"
+	"github.com/mhsanaei/3x-ui/v3/internal/database/model"
+	"github.com/mhsanaei/3x-ui/v3/internal/util/common"
+	"github.com/mhsanaei/3x-ui/v3/internal/util/link"
+
+	"gorm.io/gorm"
+)
+
+// ExternalLinkInput is one row from the client form's Links tab.
+type ExternalLinkInput struct {
+	Kind   string `json:"kind"`
+	Value  string `json:"value"`
+	Remark string `json:"remark"`
+}
+
+func (s *ClientService) GetExternalLinksForRecord(id int) ([]model.ClientExternalLink, error) {
+	var rows []model.ClientExternalLink
+	if err := database.GetDB().
+		Where("client_id = ?", id).
+		Order("sort_index ASC, id ASC").
+		Find(&rows).Error; err != nil {
+		return nil, err
+	}
+	return rows, nil
+}
+
+// normalizeExternalLinks validates and orders the incoming rows. A "link" must
+// parse to a supported share-link scheme; a "subscription" must be an http(s)
+// URL. Blank values are dropped; an invalid value is a hard error so the
+// operator gets immediate feedback instead of a silently missing config.
+func normalizeExternalLinks(inputs []ExternalLinkInput) ([]model.ClientExternalLink, error) {
+	out := make([]model.ClientExternalLink, 0, len(inputs))
+	for _, in := range inputs {
+		value := strings.TrimSpace(in.Value)
+		if value == "" {
+			continue
+		}
+		kind := strings.TrimSpace(in.Kind)
+		switch kind {
+		case model.ExternalLinkKindSubscription:
+			if !isHTTPURL(value) {
+				return nil, common.NewError("external subscription must be an http(s) URL: " + value)
+			}
+		case model.ExternalLinkKindLink, "":
+			kind = model.ExternalLinkKindLink
+			if _, err := link.ParseLink(value); err != nil {
+				return nil, common.NewError("unsupported or invalid share link: " + value)
+			}
+		default:
+			return nil, common.NewError("unknown external link kind: " + kind)
+		}
+		out = append(out, model.ClientExternalLink{
+			Kind:      kind,
+			Value:     value,
+			Remark:    strings.TrimSpace(in.Remark),
+			SortIndex: len(out),
+		})
+	}
+	return out, nil
+}
+
+func isHTTPURL(s string) bool {
+	u, err := url.Parse(s)
+	return err == nil && (u.Scheme == "http" || u.Scheme == "https") && u.Host != ""
+}
+
+// SetExternalLinksForRecord replaces a client's entire external-link set.
+func (s *ClientService) SetExternalLinksForRecord(id int, inputs []ExternalLinkInput) error {
+	rows, err := normalizeExternalLinks(inputs)
+	if err != nil {
+		return err
+	}
+	db := database.GetDB()
+	return db.Transaction(func(tx *gorm.DB) error {
+		if err := tx.Where("client_id = ?", id).Delete(&model.ClientExternalLink{}).Error; err != nil {
+			return err
+		}
+		for i := range rows {
+			rows[i].ClientId = id
+			if err := tx.Create(&rows[i]).Error; err != nil {
+				return err
+			}
+		}
+		return nil
+	})
+}
+
+func (s *ClientService) SetExternalLinksByEmail(email string, inputs []ExternalLinkInput) error {
+	if strings.TrimSpace(email) == "" {
+		return common.NewError("client email is required")
+	}
+	rec, err := s.GetRecordByEmail(nil, email)
+	if err != nil {
+		return err
+	}
+	return s.SetExternalLinksForRecord(rec.Id, inputs)
+}