All UI text across 57 files now goes through the i18n system (core/i18n.js).
Added ~120 new translation keys covering: auth, daily rewards, challenges,
ranks, shop, groups, tournaments, puzzles, orgs, emotes, and backgammon
doubling. Both ar and en dictionaries are complete and in sync.

Data strings (country names, FIDE titles, variant names, puzzle themes)
are intentionally left as-is — they use name/nameEn data pattern.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>