ShelfPlayer

Fill in missing translations across all .xcstrings files in the ShelfPlayer project. Scans every xcstrings file, identifies keys with absent or `new`/`needs_review`-state localizations, derives an auto-generated comment from the call site of the key in Swift source, and writes translations for every missing target language. Use when the user asks to "translate missing keys", "fill in translations", "complete localization", or after pulling new strings into the catalogs.