feat(update): 发行 tag 查询支持 XUI_RELEASE_LATEST_URL 覆盖（镜像/沙箱冒充发行源）

internal/web/service/panel/panel.go

@@ -601,7 +601,10 @@ func (s *PanelService) runNativeUpdate(runID int64) {
 		releaseUpdateSlot()
 	}
 
-	tag, err := fetchLatestPanelVersion()
+	client := (&service.SettingService{}).NewProxiedHTTPClient(10 * time.Minute)
+	ctx, cancel := context.WithTimeout(context.Background(), 10*time.Minute)
+	defer cancel()
+	tag, err := selfupdate.FetchLatestReleaseTag(ctx, client)
 	if err != nil {
 		fail("fetch latest release: %v", err)
 		return
@@ -622,9 +625,6 @@ func (s *PanelService) runNativeUpdate(runID int64) {
 	}
 	tmp := filepath.Join(filepath.Dir(exePath), fmt.Sprintf(".x-ui-update-%d", runID))
 	base := selfupdate.BaseURL() + tag + "/"
-	client := (&service.SettingService{}).NewProxiedHTTPClient(10 * time.Minute)
-	ctx, cancel := context.WithTimeout(context.Background(), 10*time.Minute)
-	defer cancel()
 	logger.Infof("panel self-update: downloading %s (%s)", tag, asset)
 	if err := selfupdate.DownloadVerified(ctx, client, base+asset, base+asset+".sha256", tmp); err != nil {
 		_ = os.Remove(tmp)