open_threads: new get_open_threads MCP tool on agent + manager surfaces

hive-c0re/src/agent_server.rs

@@ -174,6 +174,12 @@ async fn dispatch(req: &AgentRequest, agent: &str, coord: &Arc<Coordinator>) ->
             timing,
             file_path,
         } => handle_remind(coord, agent, message, timing, file_path.as_deref()),
+        AgentRequest::GetOpenThreads => match crate::open_threads::for_agent(coord, agent) {
+            Ok(threads) => AgentResponse::OpenThreads { threads },
+            Err(e) => AgentResponse::Err {
+                message: format!("{e:#}"),
+            },
+        },
     }
 }