Add interactive ISAC registry filters

docs/DESIGN_SYSTEM.md

@@ -356,3 +356,19 @@ returns to page one. Summary metrics remain global or filter-global and must
 never silently describe only the visible page. On narrow screens, retain
 previous, next, current page, and page-size controls before optional page
 numbers.
+
+### Registry metric filters
+
+The KPI row above an ISAC registry is an operational filter surface, not passive
+decoration. Use `KpiFilters.svelte` when each metric describes a meaningful
+record subset. The first card returns to the complete current registry or search;
+the remaining cards filter by useful classifications such as active state,
+category, equipment behavior, or restriction state.
+
+Filtering is server-backed and occurs before pagination. Filter links preserve
+compatible search and page-size parameters, reset the page number, remain
+bookmarkable, and expose the selected state with both orange emphasis and
+`aria-current`. Cards require pointer, hover, focus-visible, pressed, and
+textually identifiable active states. Counts describe the full search scope,
+not merely the visible page. Do not use aggregate facts that cannot filter the
+affected registry—replace them with actionable subsets.