feat(catalog): implement sprint 10 advanced search experience

docs/backend-platform/business-apis.md

@@ -49,6 +49,39 @@ Tenant rule:
 Must not change:
 - item identifiers/price semantics relied on frontend checkout/cart logic.
 
+## /searchitems
+Purpose:
+- keyword-based product search for catalog/search pages.
+
+High-level response shape:
+- items array
+- total count
+
+Tenant rule:
+- results must respect tenant catalog visibility and pricing policies.
+
+## /search/suggestions (future-ready)
+Purpose:
+- return instant search suggestions for typed keywords.
+
+High-level response shape:
+- suggestion strings or objects with label/value and optional popularity/count.
+
+Tenant rule:
+- suggestions generated only from tenant-visible catalog corpus.
+
+## /catalog/filters (future-ready)
+Purpose:
+- provide dynamic filter definitions and options for current search/category context.
+
+High-level response shape:
+- filter definitions
+- option counts
+- optional min/max ranges
+
+Tenant rule:
+- filter options/counts must be tenant-scoped and inventory-aware.
+
 ## /products/{id}/rating
 Purpose:
 - return product rating aggregate for engagement UI.