agent: add Remind request + ReminderTiming enum (stub implementation)

hive-c0re/src/agent_server.rs

@@ -188,5 +188,16 @@ async fn dispatch(req: &AgentRequest, agent: &str, coord: &Arc<Coordinator>) ->
                 },
             }
         }
+        AgentRequest::Remind {
+            message,
+            timing,
+            file_path,
+        } => {
+            // TODO: submit to reminder scheduler
+            // For now, return a stub response
+            AgentResponse::Err {
+                message: "remind not yet implemented".to_owned(),
+            }
+        }
     }
 }