Persist ranked-only mastery and use it consistently across progression, milestones, counts, and localized UI. Preserve mastery during history rebuilds, replay errors accurately, and generate replay-derived test profiles. Document the follow-up plan to remove the drill history cap.
Adds rust-i18n and refactors all of the text copy in the app to use the
translation function so that the UI language can be dynamically updated
in the settings.