Fix store resolution on multi-store headless Adobe Commerce setups (REVIEWS-4382)

[calsmith99]

Summary

• Pass $scopeId to getStore($scopeId) in UpdateProductFeed::execute() so URL resolution uses config scope rather than the admin HTTP hostname
• Replace $_SERVER['HTTP_HOST'] with $this->storeModel->getStore($scopeId)->getBaseUrl() so integration/app-installed receives the correct storefront URL, not the admin backend hostname
• Defer getStore() in Api constructor — store StoreManagerInterface instead of eagerly calling getStore() at DI injection time, which threw when no store view matched the admin URL

Root cause

On single-instance multi-tenant Adobe Commerce setups, the admin backend URL (mcprod.smokemart.com.au) is not registered as a store view. Magento's StoreManager::getStore() with no argument tries to resolve the current store from the HTTP hostname — finding no match, it throws "The store that was requested wasn't found."

The $scopeId was already read from the event on line 26 of UpdateProductFeed.php but never passed to getStore().

Test plan

• Save REVIEWS.io config on a standard single-store Magento setup — no regression
• Save config on a multi-store setup where admin URL differs from any store view — no exception, correct storefront URL sent to integration/app-installed
• Verify product feed URL uses storefront base URL, not admin hostname

Fixes REVIEWS-4382

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