Lychee: Webshop payment bypass via unrestricted "Dummy" gateway selection

Lychee is a free, open-source photo-management tool. Prior to 7.7.0, Lychee hides the Omnipay Dummy test provider from the checkout options in production through OmnipayFactory::get_supported_providers(), but CreateSessionRequest validates only that the submitted provider is an OmnipayProviderType and does not enforce OmnipayProviderType::isAllowed(). A buyer, including a guest when webshop_allow_guest_checkout is enabled, can submit Dummy directly and complete the test gateway flow without a real payment. When webshop_auto_fulfill_enabled is enabled, OrderCompletedListener::fullfillOrder() can then release the purchasable item. The issue requires access to the Supporter or Pro webshop and an enabled purchasable item. Testing bypassed the closed-source license middleware, so whether the real license layer performs additional payment-provider validation remains unverified. The payment finalize status check itself is not the root cause. This issue is fixed in version 7.7.0.