Translation Manager AI: forward-port check, dependency bump, v18.3.0 release

Jumoo.TranslationManager.AI: checked v17/main → v18/main forward-port status — already covered by an open PR, nothing else outstanding
Jumoo.TranslationManager.AI: bumped the Translation Manager dependency floor to the stable 18.3.0 release, dropped the Jumoo Nightly feed source now it's no longer needed, merged and cleaned up the branch
Jumoo.TranslationManager.AI: triggered a manual pre-release build to the nightly feed
Jumoo.TranslationManager.AI: released v18.3.0 to NuGet