fix(sub): deduplicate settings.clients entries per inbound in subscription output (#5134)

Multi-node sync/import drift can leave the same client twice inside an
inbound's legacy settings.clients JSON while the normalized
client_inbounds table stays clean (SyncInbound dedupes the rows it
writes but never rewrites the JSON). All three subscription builders
iterated that JSON verbatim, so every duplicate entry became a
duplicate profile in the raw, Clash, and JSON output.

Filter and dedupe by email in one shared helper (link generation keys
purely on inbound + email, so same-email entries are pure duplicates
and dropping them is lossless). The clash/json services' own
inboundService copies became unused and are removed.

internal/sub/service_dedup_test.go

@@ -0,0 +1,65 @@
+package sub
+
+import (
+	"fmt"
+	"path/filepath"
+	"testing"
+
+	"github.com/mhsanaei/3x-ui/v3/internal/database"
+	"github.com/mhsanaei/3x-ui/v3/internal/database/model"
+)
+
+// TestGetSubs_DuplicateSettingsClients_Deduped reproduces #5134: multi-node
+// sync/import drift can leave the same client twice inside an inbound's
+// legacy settings.clients JSON while the normalized client_inbounds table
+// stays clean. The subscription output must still contain one profile per
+// (inbound, client).
+func TestGetSubs_DuplicateSettingsClients_Deduped(t *testing.T) {
+	dbDir := t.TempDir()
+	t.Setenv("XUI_DB_FOLDER", dbDir)
+	if err := database.InitDB(filepath.Join(dbDir, "x-ui.db")); err != nil {
+		t.Fatalf("InitDB: %v", err)
+	}
+	t.Cleanup(func() { _ = database.CloseDB() })
+
+	const subId = "sub-dup"
+	const email = "dup@example.com"
+	const uuid = "f1b9265f-26a8-4b75-9be2-c64a94b15de1"
+
+	db := database.GetDB()
+	settings := fmt.Sprintf(`{"clients": [
+		{"id": %q, "email": %q, "subId": %q, "enable": true},
+		{"id": %q, "email": %q, "subId": %q, "enable": true}
+	]}`, uuid, email, subId, uuid, email, subId)
+	ib := &model.Inbound{
+		UserId:         1,
+		Tag:            "dup-in",
+		Enable:         true,
+		Port:           42001,
+		Protocol:       model.VLESS,
+		Settings:       settings,
+		StreamSettings: `{"network": "tcp", "security": "none"}`,
+	}
+	if err := db.Create(ib).Error; err != nil {
+		t.Fatalf("seed inbound: %v", err)
+	}
+	client := &model.ClientRecord{Email: email, SubID: subId, UUID: uuid, Enable: true}
+	if err := db.Create(client).Error; err != nil {
+		t.Fatalf("seed client: %v", err)
+	}
+	if err := db.Create(&model.ClientInbound{ClientId: client.Id, InboundId: ib.Id}).Error; err != nil {
+		t.Fatalf("seed client_inbound: %v", err)
+	}
+
+	s := NewSubService(false, "-ieo")
+	links, emails, _, _, err := s.GetSubs(subId, "sub.example.com")
+	if err != nil {
+		t.Fatalf("GetSubs: %v", err)
+	}
+	if len(links) != 1 {
+		t.Fatalf("links = %d, want 1 (duplicate settings.clients entries must collapse)", len(links))
+	}
+	if len(emails) != 1 {
+		t.Fatalf("emails = %d, want 1, got %v", len(emails), emails)
+	}
+}