Translation Manager: v17 licence fix, forward-merge, and v18.2.1 release

Translation Manager (v17): added a jumoo-translation-manager-checker/{version} user agent header to the subscription/domain licence check HttpClients, matching uSync.Complete's pattern
Forward-merged that fix from v17/main into v18/main
Released v18.2.1 to NuGet — rolls up the licence header fix plus the earlier forward-ported 17.8.1 fixes (install packaging bug, first-install set guess, single-connector auto-select)
Backfilled a missing v18.2.0 entry and release on the public Jumoo.TranslationManager.Issues changelog repo alongside the new v18.2.1 entry
Translation Manager (v17): added a clone-to-language button on the document translation status table — clones content from the current culture into an untranslated target, with a confirm dialog
Forward-merged that into v18/main, resolving conflicts with v18's translate-in-place changes