feat(mobile): integrate real backend data for profile gamification
- Add achievementsApi with methods for fetching user achievements
- Add leaguesApi with methods for league status and joining
- Update profile page to fetch real achievements and league data
- Replace mock achievements with backend-sourced data
- Add LeagueWidget showing user's league status and rank
- Fix color scheme consistency: change from light to dark theme
- Update ActivityCalendar to use semantic theme colors
- All gamification data now properly loaded from backend
Co-authored-by: Cursor cursoragent@cursor.com