fix(api): record an elapsed group as expired when its opener cancels

Cancelling the opening unpaid order ran the expiry sweep only implicitly, so a
group whose lifetime had already ended was relabelled cancelled instead of
expired. Both conditions hold in that case; sweep first so the lifetime ending
wins. The behaviour was invisible to shoppers (neither state is joinable) but it
matters to a future refund flow reading expired paid groups.

Add an integration test that reproduces the precedence.

apps/api/src/modules/group_buying/service.rs

@@ -181,12 +181,15 @@ pub async fn link_opener(tx: &mut PgConnection, group_id: Uuid, order_id: Uuid)
     repo::set_leader(tx, group_id, order_id).await
 }
 
-/// An unpaid opener cancelling closes a group that has no paid members.
+/// An unpaid opener cancelling closes a group that has no paid members. The
+/// expiry sweep runs first so an elapsed group records `expired` rather than
+/// being relabelled `cancelled`.
 pub async fn cancel_opener_group(
     tx: &mut PgConnection,
     order_id: Uuid,
     group_id: Uuid,
 ) -> ApiResult<()> {
+    repo::expire_due_groups(&mut *tx).await?;
     repo::cancel_empty_opener_group(tx, group_id, order_id).await?;
     Ok(())
 }