Resolve ARB conflicts via per-key union: apply latest Crowdin
translations for shared keys while preserving newer app keys added on
main after the branch point. Drop hyphenated ARB duplicates
(app_ar-SA, app_es-ES, app_pt-PT, app_tr-TR, app_uk-UA) that break
Flutter gen-l10n; keep underscore filenames. Add Arabic (app_ar.arb)
and regenerate app_localizations.