Address AI code review feedback from PR #5318

- Fix Makefile: Use $(CXXFLAGS) directly for consistency with build philosophy
- Fix MySQL_Catalog: Return proper error JSON instead of empty array on missing query

Makefile

@@ -155,7 +155,7 @@ build_src_debug: $(if $(LEGACY_BUILD),build_src_debug_legacy,build_src_debug_def
 # RAG ingester (PoC)
 .PHONY: rag_ingest
 rag_ingest: build_deps
-	cd RAG_POC && ${MAKE} CC=${CC} CXX=${CXX} OPTZ="${O2} -ggdb" CXXFLAGS="${O2} -ggdb"
+	cd RAG_POC && ${MAKE} CC=${CC} CXX=${CXX} CXXFLAGS="${CXXFLAGS}"
 
 .PHONY: rag_ingest_clean
 rag_ingest_clean:

lib/MySQL_Catalog.cpp

@@ -290,7 +290,8 @@ std::string MySQL_Catalog::search(
 	// FTS5 search requires a query
 	if (query.empty()) {
 		proxy_error("Catalog search requires a query parameter\n");
-		return "[]";
+		nlohmann::json error_result = {{"error", "Catalog search requires a query parameter"}};
+		return error_result.dump();
 	}
 
 	// Helper lambda to escape single quotes for SQLite SQL literals