Use expandedCalendarHeightPx to preserve full height during collapse animation,
and compute cardTopPx based on collapse state instead of offset arithmetic.
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
Add isCollapsed/collapseProgress state to CalendarViewModel for toggling
between month and week views. CalendarMonthPage animates non-selected
weeks out with offset and alpha. Introduce WeekPager for single-week
HorizontalPager and BottomCard with drag-to-collapse gesture.
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
