feat: Let modules inject admin tabs when editing a user group

[hellopablo]

Summary

• Mirrors the group-tab injector from feature/pre-new-admin onto develop.
• Adapts the implementation to the namespaced src/Admin/Controller/Groups.php controller and the current permission service.
• Removes the hard-coded legacy 2FA view and lets modules validate, render, and persist group-specific tabs.

Original feature/pre-new-admin PR: #538.

Test plan

• PHP syntax checks pass for all changed PHP files
• PHPUnit: 148 tests, 300 assertions
• Edit a group and confirm Basic Details, Password, Permissions, and injected MFA tabs render and save

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