Add a new ClientTrendChart component to render 7-day client counts.
Expose an optional chart prop on StatisticsCard and wire the chart into
the Clients Overview page using mock data

Add AreaChart/Area with gradient fill and a color prop to
ClientTrendChart (replace LineChart/Line, adjust margins and sizing).
Refactor StatisticsCard layout: make icon/description optional,
introduce trend and comparedTo props, improve loading skeleton and
inline chart display. Wire per-chart colors and trends in
page-clients-overview and remove unused icon imports.