Clicking a metric now shows a sub-team breakdown page with totals per team
(compliant, non-compliant, total, %) instead of jumping directly to a flat
device list. Clicking a sub-team then shows the device list filtered to
that team only.
Navigation flow: Overview → Vertical → Metric (sub-team totals) → Team (devices)
Backend: added optional ?team= query param to the device list endpoint for
filtered queries.
Frontend: added MetricSubTeamView component with metric-level stats bar and
clickable sub-team table. Updated navigation state to include selectedTeam.
Also updated design brief to reflect the new drill-down hierarchy.