Selected-day panel below the month grid now renders as a proper vertical
timeline: time labels in the left gutter, continuous track line with
circle markers, and white cards for each item. All-day tasks and events
get a stroke circle; timed entries get a solid colored dot; workout gets
a dumbbell icon; completed items show a checkmark circle with strikethrough.
Tasks can be toggled directly from the timeline card. Cal events show
end time as subtitle. Empty state shows a calendar icon.
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