- Habits and the account now accumulate XP and levels from check streaks, with
streak/level-up celebration banners and push notifications.
- The "yesterday missed" banner on /today now lets a habit be explicitly marked
failed (not just checked done), backed by a new HabitLog.status column so
completion-rate/streak calculations never count a failed day as done.
- The habit management tabs scroll horizontally on narrow screens instead of
wrapping to two lines, with a pure-CSS edge shadow indicating more content.
