feat: improve commerce checkout flow

supabase/migrations/202606290006_commerce_checkout_experience.sql

@@ -0,0 +1,13 @@
+create unique index if not exists idx_coupon_redemptions_user_coupon_once
+  on public.coupon_redemptions(tenant_id, user_id, coupon_id)
+  where coupon_id is not null;
+
+create index if not exists idx_coupon_redemptions_order_user
+  on public.coupon_redemptions(tenant_id, order_id, user_id)
+  where order_id is not null;
+
+create index if not exists idx_payments_order_updated
+  on public.payments(tenant_id, order_id, updated_at desc);
+
+create index if not exists idx_order_items_order
+  on public.order_items(tenant_id, order_id);