When a day is closed, re-closed, or reopened, DayService now
recomputes worked_ms and delta_ms on the closed week containing
that day (if the week is already closed). This prevents stale
delta values after editing entries and re-closing a day.
- DayService.recomputeWeek: sums worked_ms from all closed_days
in the week, updates closed_weeks row preserving expected_ms
- NewDayService now takes ClosedWeekStore
- WeekKeyForDayKey exported helper (used by DayService)
- TestWeekSnapshotUpdatesWhenDayReopened regression test
