fix(panel): stop the task status dropdown duplicating the current status

The status Select always renders the current status as its first item, then
appends the valid-transitions list. When a task changed state (e.g. on
approve-and-merge to completed) the cached valid-transitions query was not
refetched, so it still held the previous state's targets — which include the
now-current status. That yields two SelectItems with the same value; Radix
requires unique values, so the list showed a duplicate entry and the trigger
label rendered doubled ("Completed Completed").

Key the valid-transitions query on the task status so it refetches on every
state change, and filter the current status out of the appended list so it can
never duplicate the always-rendered current item.

panel/src/components/tasks/task-detail/task-header.tsx

@@ -97,8 +97,14 @@ export function TaskHeader({ task, onAction }: TaskHeaderProps) {
   const updateTask = useUpdateTask();
   // Fetch valid next statuses from GET /tasks/{id}/valid-transitions.
   // Falls back to [] while loading or on error — the Select is disabled during loading.
-  const { data: validTransitionsData, isLoading: isTransitionsLoading } = useTaskValidTransitions(task.id);
-  const nextStatuses: TaskStatus[] = validTransitionsData ?? [];
+  const { data: validTransitionsData, isLoading: isTransitionsLoading } = useTaskValidTransitions(task.id, task.status);
+  // Exclude the current status: it is always rendered first (below), so a stale
+  // cache or a backend list that re-includes it would duplicate the item. Radix
+  // Select requires unique item values, so a duplicate also garbles the trigger
+  // label (it renders as e.g. "Completed Completed").
+  const nextStatuses: TaskStatus[] = (validTransitionsData ?? []).filter(
+    (s) => s !== task.status
+  );
   const [deleteOpen, setDeleteOpen] = useState(false);
 
   // Inline editing states