feat: add memory citation to agent message (#14821)

Client side to come

codex-rs/core/src/event_mapping.rs

@@ -83,7 +83,12 @@ fn parse_agent_message(
         }
     }
     let id = id.cloned().unwrap_or_else(|| Uuid::new_v4().to_string());
-    AgentMessageItem { id, content, phase }
+    AgentMessageItem {
+        id,
+        content,
+        phase,
+        memory_citation: None,
+    }
 }
 
 pub fn parse_turn_item(item: &ResponseItem) -> Option<TurnItem> {