MetricCardComponent

Compact KPI/metric primitive for dashboard summaries — mutable `value`/`delta`/`trend` state via a single `set-value` action, distinct from the mostly-static dashboard primitives around it.

public static function contract(): Milpa\Live\ValueObjects\ComponentContract

This primitive's runtime contract (`title`/`value`/`delta`/`trend` props, `set-value` action).