Feature: Reusable MultiFactorChallenge class

[webard]

Description

The Pull Request extracts OTP functionality from Login into a separate MultiFactorChallenge class, making it possible to use this functionality outside the Login page.

The motivation for this change is work on a solution that allows actions to be confirmed with a one-time code. This is very useful for actions such as destructive operations.

Of course, this can be achieved without this change, but while working on it I thought that extracting this functionality into an external class would let authors reuse it in their own solutions.

The translation key stayed under login. The provider switcher still uses filament-panels::auth/pages/login.multi_factor.form.provider.label, even though the component no longer lives in Login. Moving the key would touch all localization files and would cause a regression in languages where the translation has not been added yet. I’m happy to move it if you prefer.

MultiFactorAuthenticationProvider::getLoginFormLabel() is now used outside login. The name no longer fully matches the usage, but renaming a method in a public interface would break providers outside core, so I’m leaving it unchanged.

Functional changes

• Code style has been fixed by running the composer cs command.
• Changes have been tested to not break existing functionality.
• Documentation is up-to-date.