Since the freely scrolling views (#759) the day, week and month views are
positioned by their own focus rather than by the selected date, and a grid
click deliberately only marks a day that is already on screen. The mini
calendar shared that handler, so picking a day there highlighted it but
left the view where it was. Give it its own handler that jumps to the day
(keeping the mobile month-to-day switch), the same path the prev/next/today
controls and deep links use.