feat(search_tool): gate search_tool on model supports_search_tool field (#14502)

codex-rs/codex-api/tests/models_integration.rs

@@ -95,6 +95,7 @@ async fn models_client_hits_models_endpoint() {
             input_modalities: default_input_modalities(),
             prefer_websockets: false,
             used_fallback_model_metadata: false,
+            supports_search_tool: false,
         }],
     };