manager: scope GetLooseEnds to manager's own items

hive_wide returns ALL agents' reminders and questions, causing other
agents' reminders (e.g. triage) to appear on the manager's web page
and in the get_loose_ends MCP tool. The MCP tool spec says it shows
your own pending items — switch to for_agent(MANAGER_AGENT) which
includes all approvals (manager is sole submitter), questions where
the manager is asker/target, and only the manager's own reminders.

Fixes #118

hive-c0re/src/manager_server.rs

@@ -396,7 +396,7 @@ async fn dispatch(req: &ManagerRequest, coord: &Arc<Coordinator>) -> ManagerResp
                 },
             }
         }
-        ManagerRequest::GetLooseEnds => match crate::loose_ends::hive_wide(coord) {
+        ManagerRequest::GetLooseEnds => match crate::loose_ends::for_agent(coord, MANAGER_AGENT) {
             Ok(loose_ends) => ManagerResponse::LooseEnds { loose_ends },
             Err(e) => ManagerResponse::Err {
                 message: format!("{e:#}"),