Improve selling plan visibility control and sync with Shopify (Shop app)

Selling plan visibility is inconsistent between Subi and external Shopify surfaces like the Shop app. Current issues: Deactivating a selling plan in Subi does not remove it from Shopify, causing inactive plans to still appear in the Shop app Merchants lack control over which plans are exposed in the Shop channel There is no reliable way to immediately hide or sync plan visibility across channels This can lead to customers purchasing inactive or test plans. A solution is needed to ensure proper synchronization and give merchants full control over selling plan visibility across all channels.