Add Greek language localization

### Description of the new feature / enhancement

Currently the app is missing Greek altogether; adding it would be helpful.

### Scenario when this would be used?

Always, everywhere.

### Supporting information

_No response_

No files, tests, or entry points are named. Start by locating the existing localization resources and how supported languages are registered, then determine the full set of app surfaces that require Greek. Done means Greek is selectable and translations are available throughout the app without missing-resource fallbacks.

Written by the indexing model from the issue text.