Clicking the Non-Compliant card on the CCP Metrics overview now toggles a
panel of metric buttons below it, each showing the metric ID, category,
non-compliant count, and compliance % vs target. Styled like the compliance
page's MetricHealthCard pattern.
Backend: added metric_breakdown to the /stats response — aggregated
cross-vertical metric totals (ALL: rows only, grouped by metric_id).
Also updated tech steering file to document the single-port Express
architecture and the requirement to run npm run build after frontend changes.
