feat(catalog): implement sprint 10 advanced search experience

docs/platform/06-api-contracts.md

@@ -39,6 +39,17 @@
 Правило:
 - Feature UI не вызывает API напрямую; запросы идут через ProductFacade -> domain service -> provider/repository.
 
+## Advanced Catalog/Search Expectations
+- Suggestions endpoint (future-ready):
+  - GET /search/suggestions?q={term}
+  - response: suggestion strings with optional popularity/count metadata.
+- Dynamic filter metadata endpoint (future-ready):
+  - GET /catalog/filters?category={id}&q={term}
+  - response: filter definitions/options that frontend can render without hardcoded filter schema.
+- Sort extension contract:
+  - Backend may introduce new sort IDs via bootstrap `catalog.availableSorts`.
+  - Frontend must render unknown sort keys safely if label mapping is provided.
+
 ## Пример API ответа: категории
 ```json
 {