v2.18.1 - Fix: frequency habit check-in progress

Fixed

• Checking in an "x times a week" habit now updates its "n/x this week" count and the current-week strip cell immediately. Previously the streak flame moved but the weekly progress stayed stale (and the week cell stayed grey) until the next background refresh - and a second check-in in the same week could briefly show the wrong streak. The optimistic update is now frequency-aware (#76).