Update agenda

Author: wesbland

_data/meetings/2025/09/agenda.yml

@@ -28,9 +28,9 @@ plenaries:
       presenter: All WG chairs or their proxies
       done: 0
 
-    - type: Reading
-      title: Placeholder Reading
-      issue_number: 1234
-      presenter: Placeholder Presenter
+    - type: Plenary
+      title: "Concepts for designing modern C++ interfaces for MPI"
+      link: https://www.arxiv.org/abs/2506.14610
+      presenter: Tony
       done: 0