v2.18.0 - Habits v2 Step 2 (frequency + deadline-free schedules)

Added

• "X times a week" habits (#75) - a habit's schedule can now be a weekly frequency ("go to the gym 3x a week") instead of fixed days. Pick the mode in the habit's Schedule chip: Specific days (the existing "every Tue & Thu") or x times a week (a 1-7 stepper). A frequency habit is checkable any day; its card shows "n/x this week", a week-based streak, and a strip of recent weeks coloured green (target met), yellow (showed up but under target), or grey (missed). The streak counts consecutive weeks you showed up at least once - hitting the full target turns the week green, but a yellow week still keeps the streak alive; only a fully missed week breaks it.
• Claude can set the frequency over the connector: create_task / update_task accept a weeklyTarget (1-7).

Changed

• Habits no longer need a deadline to have a schedule (#75). A habit's recurrence is its check-in pattern, not a due date, so the Due chip is hidden for habits and you can set a schedule with no deadline. (Ordinary recurring tasks still need a deadline - it's the anchor they advance from on completion.)

Notes

• Small database migration: one nullable WeeklyTarget column; existing habits are untouched and stay on the specific-days/daily model. A habit is one mode or the other (specific-days OR a weekly target), never both. Deferred to a later pass: a combined "x times among chosen days" mode, an "x times a month" period, and the calendar heatmap.