Fix 2FA admin emails silently suppressed when default store has email disabled

[thai2301]

Description

EmailUserNotifier::sendConfigRequired() renders its 2FA-instructions email for 'area' => 'adminhtml', 'store' => 0, but that option only affects the template's locale/content. Whether the email actually gets sent is decided by a completely separate, global plugin in Magento core: Magento\Email\Model\Mail\TransportInterfacePlugin::aroundSendMessage(), which checks:

$this->scopeConfig->isSetFlag('system/smtp/disable', ScopeInterface::SCOPE_STORE)

with no explicit scope code. That resolves against whatever store StoreManagerInterface::getStore() considers "current" at that moment — in a live adminhtml request (no frontend store context), Magento's store resolution falls through to the default store of the default website, not store 0. If that store specifically has email communication disabled, every 2FA notification is silently swallowed, even though this email is architecturally meant to be governed by the global/default scope.

This mirrors a very similar, already-fixed bug in Magento\ProductAlert\Model\Email::send() (ticket ACP2E-4870, "Product Alert Consumer ignores store scoped system/smtp/disable"), which wraps its own sendMessage() call in App\Emulation::startEnvironmentEmulation()/stopEnvironmentEmulation() so the ambient store the suppression check reads actually matches the store the email was built for.

This PR applies the same pattern here, emulating Store::DEFAULT_STORE_ID / Area::AREA_ADMINHTML around the sendMessage() call, so the plugin's scope-less check resolves to the same global scope this notification is rendered for, instead of an unrelated frontend store. The TransportInterfacePlugin itself is intentionally left untouched — it's a shared plugin wrapping every outgoing email in Magento, and changing its scope resolution would break legitimate per-store suppression for genuinely store-scoped emails (newsletters, product alerts, etc., including the ACP2E-4870 fix it relies on).

Related Issue

Fixes magento/magento2#40969

Manual testing scenarios

1. Set system/smtp/disable (Store Email Addresses config or direct core_config_data row) to 1 for a specific store, e.g. the default store of the default website.
2. Enable 2FA and create/edit an admin user so a "configuration required" 2FA email would normally be triggered.
3. Before this fix: the email is silently not sent, no error surfaced. After this fix: the email sends normally, since the suppression check now correctly reads the default/global scope rather than the disabled store's scope.

Questions or comments

None.

Contribution checklist

• Pull request has a meaningful description of its purpose
• All existing and new tests pass
• Static tests pass
• Ensured backward compatibility

[thai2301]

@magento run all tests

[thai2301]

@magento run all tests

[thai2301]

@magento run Unit Tests, Functional Tests B2B

[thai2301]

@magento run all tests