BatchUpdateView now accepts a saveDate parameter. When saving from a past-month
check-in, the call site passes referenceDate.endOfMonth so snapshots are dated
within the correct month instead of today. For the current month, Date() is used.
Widget forward-fills missing month buckets (trend and category series) using the
most recent earlier month's value, preventing gaps when a check-in is done in the
following month.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>