manager: add optional agent param to GetLooseEnds

GetLooseEnds now takes agent: Option<String>:
- None   = manager's own loose ends (default; the bug fix)
- Some("*")    = hive-wide view (every approval/question/reminder)
- Some("name") = that agent's loose ends

The get_loose_ends MCP tool exposes this as an optional agent arg, so
the manager can still scan the whole swarm on demand. The web UI and
post-turn counts pass None (manager's own).

hive-c0re/src/manager_server.rs

@@ -396,12 +396,19 @@ async fn dispatch(req: &ManagerRequest, coord: &Arc<Coordinator>) -> ManagerResp
                 },
             }
         }
-        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:#}"),
-            },
-        },
+        ManagerRequest::GetLooseEnds { agent } => {
+            let result = match agent.as_deref() {
+                Some("*") => crate::loose_ends::hive_wide(coord),
+                Some(name) => crate::loose_ends::for_agent(coord, name),
+                None => crate::loose_ends::for_agent(coord, MANAGER_AGENT),
+            };
+            match result {
+                Ok(loose_ends) => ManagerResponse::LooseEnds { loose_ends },
+                Err(e) => ManagerResponse::Err {
+                    message: format!("{e:#}"),
+                },
+            }
+        }
         ManagerRequest::CountPendingReminders => {
             match coord.broker.count_pending_reminders_for(MANAGER_AGENT) {
                 Ok(count) => ManagerResponse::PendingRemindersCount { count },