Add dashboard drill-down and metric formula visibility

Dashboard metrics should expose what data is included and allow deeper inspection of the underlying records.

Transcript Context

The team asked for a way to click into dashboard stats and understand where the number comes from. They distinguished two needs: first, seeing the formula or definition behind a metric, including what is in or out of scope and what date range is being used; second, being able to inspect the underlying orders when someone wants more than the surface-level number. The goal is not only verification, but also being able to investigate why a metric looks the way it does.