reminder: add background scheduler loop - checks & delivers due reminders every 5s

hive-c0re/src/coordinator.rs

@@ -118,6 +118,10 @@ impl Coordinator {
         }
     }
 
+    pub fn list_agents(&self) -> Vec<String> {
+        self.agents.lock().unwrap().keys().cloned().collect()
+    }
+
     /// Mark an agent as in-progress (only one state per agent for now).
     pub fn set_transient(&self, name: &str, kind: TransientKind) {
         self.transient.lock().unwrap().insert(