Tool for showing localization slots to owner

We could have a special mode for the owner, accessed through e.g. a button, to show the localization keys in use for texts, including the ones that are currently empty and hidden. This would help in customizing the localizations and texts.

The issue does not identify files, tests, or an entry point. Start by tracing how owner-facing UI controls and localization keys are currently handled; done means an owner-only mode can reveal all in-use keys, including empty and hidden texts, for customization.

Written by the indexing model from the issue text.